Linux CLI 43 🐧 cut paste and join commands - KandZ

cut -d ' ' -f 1 data.txt
cut -d ' ' -f 1,3 data.txt
cut -c 1-3 example.txt

cat data.txt
cat example.txt
paste data.txt example.txt
paste -d ',' data.txt example.txt
paste data.txt example.txt > csvfile.csv
cat csvfile.csv

cat file1.txt
cat file2.txt
join file1.txt file2.txt
join -v 1 file1.txt file2.txt
join -a 1 file1.txt file2.txt

cut, paste, and join are the column-level tools of the Unix text toolbox. cut pulls fields out of each line, paste puts lines from multiple files side by side, and join combines two files on a shared key — like a miniature SQL join at the command line.

Key point: These tools work on structured text — files organized into columns or fields. cut and paste are about layout; join is about relational matching. Together they handle most of what you’d otherwise reach for a spreadsheet or database to do.

a – cut command

cut is used to extract sections from each line of input. Extraction is based on delimiters and field positions. It is mainly used for processing text files — logs, CSVs, /etc/passwd, and anything else with columns.

Syntax:

cut [options] [file...]

Common options:

Option	Purpose
`-f N`	Extract field N
`-f N,M`	Extract fields N and M
`-f N-M`	Extract a range of fields
`-d CHAR`	Use CHAR as the delimiter (default: TAB)
`-c N-M`	Extract characters N through M
`-b N-M`	Extract bytes N through M
`--complement`	Print everything except the selected fields
`-s`	Suppress lines with no delimiter
`--output-delimiter=STR`	Use STR between output fields

Examples:

# Look at the data first
$ cat data.txt
alice 95 A
bob 87 B
charlie 92 A
dave 78 C

# Extract the first field (space-delimited)
$ cut -d ' ' -f 1 data.txt
alice
bob
charlie
dave

# Extract fields 1 and 3
$ cut -d ' ' -f 1,3 data.txt
alice A
bob B
charlie A
dave C

# Extract a range of fields (1 through 3)
$ cut -d ' ' -f 1-3 data.txt
alice 95 A
bob 87 B
charlie 92 A
dave 78 C

# Everything except field 2
$ cut -d ' ' -f 2 --complement data.txt
alice A
bob B
charlie A
dave C

# Extract characters 1-3 of each line
$ cat example.txt
hello world
goodbye moon
hi there

$ cut -c 1-3 example.txt
hel
goo
hi

# Extract specific characters
$ cut -c 1,3,5 example.txt
hlo
gob
h hr

# Use a different delimiter — colon
$ cut -d ':' -f 1,3 /etc/passwd | head -3
root:0
daemon:1
bin:2

# Change the output delimiter
$ cut -d ':' -f 1,3 --output-delimiter=',' /etc/passwd | head -3
root,0
daemon,1
bin,2

# Suppress lines with no delimiter
$ printf "a b\nno_delim\nc d\n" | cut -d ' ' -f 1 -s
a
c

-f vs -c — fields vs characters:

Mode	What it does	Use when
`-f`	Splits by delimiter, selects fields	Structured columns
`-c`	Selects character positions	Fixed-width data

# Fixed-width data — use -c
$ cat fixed.txt
2024-01-15T10:00:00
2024-01-16T11:30:00

$ cut -c 1-10 fixed.txt
2024-01-15
2024-01-16

Note: cut requires a single-character delimiter. For multi-character delimiters (like :: or , ), use awk -F instead. Also, cut doesn’t understand quotes — a comma inside a quoted CSV field will break it.

b – paste command

paste merges lines of files side by side. It reads data from each file and writes it to standard output. By default, each line from each file is separated by a TAB character.

Syntax:

paste [options] [file...]

Common options:

Option	Purpose
`-d 'CHAR'`	Use CHAR as the delimiter (default: TAB)
`-s`	Merge files in series (one file per line)
`-`	Read from stdin

Examples:

# Look at the files
$ cat data.txt
alice
bob
charlie

$ cat example.txt
95
87
92

# Merge side by side (TAB separated)
$ paste data.txt example.txt
alice	95
bob	87
charlie	92

# Use a comma as the delimiter
$ paste -d ',' data.txt example.txt
alice,95
bob,87
charlie,92

# Save to a file
$ paste -d ',' data.txt example.txt > csvfile.csv
$ cat csvfile.csv
alice,95
bob,87
charlie,92

# Series mode — all of file1 on one line, then all of file2
$ paste -s data.txt example.txt
alice	bob	charlie
95	87	92

# Series mode with a delimiter
$ paste -s -d ',' data.txt
alice,bob,charlie

# Cycle through multiple delimiters
$ paste -d ',;' data.txt example.txt
alice,95
bob;87
charlie,92

# Combine more than two files
$ paste data.txt example.txt example.txt
alice	95	95
bob	87	87
charlie	92	92

# Paste from stdin with -
$ echo "extra" | paste data.txt -
alice	extra
bob	
charlie

paste vs cat:

Command	Effect
`cat a.txt b.txt`	Concatenates — file B below file A
`paste a.txt b.txt`	Merges — file B beside file A

cat a.txt b.txt          paste a.txt b.txt
┌──────────┐             ┌──────────┐
│ a1       │             │ a1  b1   │
│ a2       │             │ a2  b2   │
│ a3       │             │ a3  b3   │
│ b1       │             └──────────┘
│ b2       │
│ b3       │
└──────────┘

Tip: paste is perfect for building CSVs from separate column files, or for adding a line number next to each line: paste <(seq 1 10) file.txt.

c – join command

join combines lines from two files on the basis of one or more fields. By default it assumes the first field is the join key. Files need to be sorted on that key for join to work correctly — just like uniq.

Syntax:

join [options] file1 file2

Common options:

Option	Purpose
`-a N`	Display unmatched lines from file N
`-v N`	Display only unmatched lines from file N
`-t CHAR`	Use CHAR as the field delimiter
`-i`	Ignore case
`-1 N`	Join on field N of file 1
`-2 N`	Join on field N of file 2
`-o FORMAT`	Specify output fields
`-e STR`	Replace missing fields with STR

Examples:

# Look at the files
$ cat file1.txt
1 alice
2 bob
3 charlie
4 dave

$ cat file2.txt
1 95
2 87
3 92
5 78

# Join on the first field (default)
$ join file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
# Note: "4 dave" and "5" have no match, so they're omitted

# Show unmatched lines from file 1
$ join -a 1 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
4 dave
# "4 dave" is included with no match

# Show unmatched lines from file 2
$ join -a 2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
5 78

# Show only unmatched lines from file 1
$ join -v 1 file1.txt file2.txt
4 dave

# Show only unmatched lines from file 2
$ join -v 2 file1.txt file2.txt
5 78

# Show unmatched from BOTH files
$ join -a 1 -a 2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
4 dave
5 78

# Use a comma delimiter
$ cat f1.csv
1,alice
2,bob
3,charlie

$ cat f2.csv
1,95
2,87
3,92

$ join -t ',' f1.csv f2.csv
1,alice,95
2,bob,87
3,charlie,92

# Join on a different field
$ cat users.txt
alice 1
bob 2
charlie 3

$ cat scores.txt
95 1
87 2
92 3

$ join -1 2 -2 2 users.txt scores.txt
1 alice 95
2 bob 87
3 charlie 92

# Ignore case
$ join -i file1.txt file2.txt

# Custom output format
$ join -o 1.1,1.2,2.2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92

# Replace missing fields
$ join -a 1 -e "N/A" -o 1.1,1.2,2.2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
4 dave N/A

Why sorting matters:

┌──────────────────────────────────────────────┐
│           Unsorted input                     │
│                                              │
│  file1:      file2:                          │
│  3 charlie   1 95                            │
│  1 alice     3 92                            │
│  2 bob       2 87                            │
│                                              │
│  join walks both files in parallel,          │
│  comparing current keys. Unsorted = chaos.   │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│           Sorted input                       │
│                                              │
│  file1:      file2:                          │
│  1 alice     1 95                            │
│  2 bob       2 87                            │
│  3 charlie   3 92                            │
│                                              │
│  join matches 1-1, 2-2, 3-3 cleanly          │
│                                              │
└──────────────────────────────────────────────┘

Always sort both files on the join key first: sort -k1,1 file1 > f1.sorted then join f1.sorted f2.sorted. The default sort on the whole line usually works if the key is the first field.

Complete Example Session

# ============================================
# PART 1: CUT — EXTRACT FIELDS
# ============================================

$ cat data.txt
alice 95 A
bob 87 B
charlie 92 A
dave 78 C

$ cut -d ' ' -f 1 data.txt
alice
bob
charlie
dave

$ cut -d ' ' -f 1,3 data.txt
alice A
bob B
charlie A
dave C

# ============================================
# PART 2: CUT — EXTRACT CHARACTERS
# ============================================

$ cat example.txt
hello world
goodbye moon
hi there

$ cut -c 1-3 example.txt
hel
goo
hi

# ============================================
# PART 3: CUT ON /etc/passwd
# ============================================

$ cut -d ':' -f 1,3 /etc/passwd | head -5
root:0
daemon:1
bin:2
sys:3
sync:4

# ============================================
# PART 4: PASTE — MERGE SIDE BY SIDE
# ============================================

$ cat data.txt
alice
bob
charlie

$ cat example.txt
95
87
92

$ paste data.txt example.txt
alice	95
bob	87
charlie	92

$ paste -d ',' data.txt example.txt
alice,95
bob,87
charlie,92

$ paste -d ',' data.txt example.txt > csvfile.csv
$ cat csvfile.csv
alice,95
bob,87
charlie,92

# ============================================
# PART 5: PASTE — SERIES MODE
# ============================================

$ paste -s data.txt example.txt
alice	bob	charlie
95	87	92

$ paste -s -d ',' data.txt
alice,bob,charlie

# ============================================
# PART 6: JOIN — BASIC
# ============================================

$ cat file1.txt
1 alice
2 bob
3 charlie
4 dave

$ cat file2.txt
1 95
2 87
3 92
5 78

$ join file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92

# ============================================
# PART 7: JOIN — UNMATCHED LINES
# ============================================

$ join -v 1 file1.txt file2.txt
4 dave

$ join -a 1 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
4 dave

$ join -a 1 -a 2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92
4 dave
5 78

# ============================================
# PART 8: COMBINED PIPELINE
# ============================================

# Build a report: username, uid, shell
$ cut -d ':' -f 1,3,7 /etc/passwd | head -5
root:0:/bin/bash
daemon:1:/usr/sbin/nologin
bin:2:/usr/sbin/nologin
sys:3:/usr/sbin/nologin
sync:4:/bin/sync

# CSV from two columns
$ paste -d ',' <(cut -d: -f1 /etc/passwd) <(cut -d: -f3 /etc/passwd) | head -5
root,0
daemon,1
bin,2
sys,3
sync,4

# Join users with their shells
$ cut -d: -f1,3 /etc/passwd | sort -k1,1 > users.txt
$ cut -d: -f1,7 /etc/passwd | sort -k1,1 > shells.txt
$ join users.txt shells.txt | head -5
root 0 /bin/bash
daemon 1 /usr/sbin/nologin
bin 2 /usr/sbin/nologin
sys 3 /usr/sbin/nologin
sync 4 /bin/sync

Quick Reference

cut

Command	Purpose
`cut -d ' ' -f 1 FILE`	First field
`cut -d ' ' -f 1,3 FILE`	Fields 1 and 3
`cut -d ' ' -f 1-3 FILE`	Range of fields
`cut -d ' ' -f 2 --complement FILE`	All but field 2
`cut -c 1-3 FILE`	First 3 characters
`cut -c 1,3,5 FILE`	Specific characters
`cut -d ':' -f 1 /etc/passwd`	Colon-delimited field
`cut -d ':' -f 1,3 --output-delimiter=',' FILE`	Custom output delimiter
`cut -d ' ' -f 1 -s FILE`	Suppress lines without delimiter

paste

Command	Purpose
`paste A B`	Merge side by side (TAB)
`paste -d ',' A B`	Merge with comma
`paste -s A`	All lines of A on one line
`paste -s -d ',' A`	Series with comma
`paste A B > out.csv`	Save merged output
`paste -d ',;' A B`	Cycle delimiters
`paste A -`	Merge A with stdin

join

Command	Purpose
`join A B`	Join on first field
`join -a 1 A B`	Include unmatched from A
`join -a 2 A B`	Include unmatched from B
`join -a 1 -a 2 A B`	Include all unmatched
`join -v 1 A B`	Only unmatched from A
`join -t ',' A B`	Custom delimiter
`join -i A B`	Case-insensitive
`join -1 N -2 M A B`	Join on different fields
`join -o 1.1,1.2,2.2 A B`	Custom output format
`join -e STR -a 1 A B`	Fill missing fields

Tool Comparison

Tool	Direction	Purpose
`cut`	Vertical	Extract fields/columns
`paste`	Horizontal	Merge files side by side
`join`	Relational	Match on shared key

Best Practices

✅ Do This:

# Use -d to set the delimiter explicitly
cut -d ' ' -f 1 data.txt              # ✅

# Use -s to skip lines without delimiter
cut -d ' ' -f 1 -s data.txt           # ✅

# Use paste to build CSVs from columns
paste -d ',' col1.txt col2.txt > out.csv  # ✅

# Sort both files before join
sort -k1,1 f1 > f1.sorted
sort -k1,1 f2 > f2.sorted
join f1.sorted f2.sorted              # ✅

# Use -a 1 -a 2 to include all lines
join -a 1 -a 2 f1 f2                  # ✅

# Use process substitution to feed cut into paste
paste <(cut -d: -f1 /etc/passwd) <(cut -d: -f3 /etc/passwd)  # ✅

# Verify with a small sample first
head file.txt | cut -d ' ' -f 1       # ✅

❌ Don’t Do This:

# Don't use cut with multi-character delimiters
cut -d '::' -f 1 file.txt             # ❌ only first char used

# Don't use cut for quoted CSV fields
cut -d ',' -f 2 data.csv              # ❌ breaks on "a,b"

# Don't forget to sort before join
join f1 f2                            # ❌ wrong results if unsorted

# Don't confuse -a and -v
join -v 1 f1 f2                       # ✅ only unmatched
join -a 1 f1 f2                       # ✅ matched + unmatched

# Don't paste files with different line counts blindly
paste short.txt long.txt              # ⚠️  short lines padded with tabs

# Don't use cut when awk is clearer
cut -d ' ' -f 2- file.txt             # ⚠️  works, but awk is cleaner

Common Pitfalls

Pitfall	Problem	Solution
Multi-char delimiter	`cut` uses only the first char	Use `awk -F`
Unsorted `join` input	Wrong or missing matches	`sort` first
Quoted CSV	`cut` breaks on commas in quotes	Use a real CSV parser
TAB vs spaces	Default delimiter is TAB	Specify `-d ' '`
`-a` vs `-v` confusion	Wrong set of lines	`-a` = include, `-v` = only
Field numbering	Starts at 1	`-f 1` = first field
Empty lines	`paste` pads with tabs	Pre-filter blank lines
Range overlap	`-f 1-3,2` is redundant	Use `-f 1-3`

Real-World Examples

1. Extract Usernames from `/etc/passwd`

$ cut -d ':' -f 1 /etc/passwd | head -5
root
daemon
bin
sys
sync

2. Extract Username and UID

$ cut -d ':' -f 1,3 /etc/passwd | head -5
root:0
daemon:1
bin:2
sys:3
sync:4

3. Build a CSV from Two Columns

$ paste -d ',' <(cut -d: -f1 /etc/passwd) <(cut -d: -f3 /etc/passwd) | head -5
root,0
daemon,1
bin,2
sys,3
sync,4

4. Add Line Numbers to a File

$ paste <(seq 1 5) file.txt
1	line one
2	line two
3	line three
4	line four
5	line five

5. Convert a Column into a Single Line

$ paste -s -d ',' data.txt
alice,bob,charlie,dave

6. Join Users with Their Scores

$ sort -k1,1 users.txt > u.sorted
$ sort -k1,1 scores.txt > s.sorted
$ join u.sorted s.sorted
alice 95
bob 87
charlie 92

7. Show Users Without Scores

$ join -v 1 u.sorted s.sorted
dave

8. Full Outer Join

$ join -a 1 -a 2 u.sorted s.sorted
alice 95
bob 87
charlie 92
dave
eve 78

9. Join with a Different Delimiter

$ join -t ',' f1.csv f2.csv
1,alice,95
2,bob,87
3,charlie,92

10. Extract Fixed-Width Columns

$ cat fixed.txt
2024-01-15T10:00:00 ERROR disk
2024-01-16T11:30:00 WARN cpu

$ cut -c 1-10,21-25 fixed.txt
2024-01-15ERROR
2024-01-16WARN

11. Merge Multiple Files Side by Side

$ paste name.txt age.txt city.txt
alice	30	Paris
bob	25	London
charlie	35	Berlin

12. Join and Format Output

$ join -o 1.1,1.2,2.2 file1.txt file2.txt
1 alice 95
2 bob 87
3 charlie 92

13. Filter Columns and Reorder

$ cut -d ':' -f 3,1 /etc/passwd | head -3
0:root
1:daemon
2:bin

14. Combine cut + sort + uniq

# Unique shells used on the system
$ cut -d ':' -f 7 /etc/passwd | sort -u
/bin/bash
/bin/sync
/usr/sbin/nologin

15. Build a Report from `/etc/passwd`

$ paste -d ',' \
    <(cut -d: -f1 /etc/passwd) \
    <(cut -d: -f3 /etc/passwd) \
    <(cut -d: -f7 /etc/passwd) | head -5
root,0,/bin/bash
daemon,1,/usr/sbin/nologin
bin,2,/usr/sbin/nologin
sys,3,/usr/sbin/nologin
sync,4,/bin/sync

Visual: cut vs paste vs join

┌──────────────────────────────────────────────┐
│                  cut                         │
│                                              │
│  Input:     Output (field 1):                │
│  a1 a2 a3   a1                               │
│  b1 b2 b3   b1                               │
│  c1 c2 c3   c1                               │
│                                              │
│  Extracts columns vertically                 │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│                 paste                        │
│                                              │
│  File A:   File B:     Output:               │
│  a1        b1          a1  b1                │
│  a2        b2          a2  b2                │
│  a3        b3          a3  b3                │
│                                              │
│  Merges files horizontally                   │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│                  join                        │
│                                              │
│  File A:      File B:     Output:            │
│  1 alice      1 95        1 alice 95         │
│  2 bob        2 87        2 bob 87           │
│  3 charlie    3 92        3 charlie 92       │
│                                              │
│  Matches rows on a shared key                │
│                                              │
└──────────────────────────────────────────────┘

Summary

Command	Purpose	Example
`cut -d ' ' -f 1 FILE`	First field	`cut -d ' ' -f 1 data.txt`
`cut -d ' ' -f 1,3 FILE`	Fields 1 and 3	`cut -d ' ' -f 1,3 data.txt`
`cut -c 1-3 FILE`	First 3 chars	`cut -c 1-3 example.txt`
`cut -d ':' -f 1 /etc/passwd`	Colon field	`cut -d: -f1 /etc/passwd`
`cut -f 2 --complement FILE`	All but field 2	`cut -d ' ' -f 2 --complement f`
`cut -d ' ' -f 1 -s FILE`	Suppress no-delim lines	`cut -d ' ' -f 1 -s f`
`paste A B`	Merge side by side	`paste data.txt example.txt`
`paste -d ',' A B`	Merge with comma	`paste -d ',' a.txt b.txt`
`paste -s A`	All on one line	`paste -s data.txt`
`paste A B > out.csv`	Save merged output	`paste a b > out.csv`
`join A B`	Join on first field	`join file1.txt file2.txt`
`join -a 1 A B`	Include unmatched from A	`join -a 1 f1 f2`
`join -a 1 -a 2 A B`	Include all unmatched	`join -a 1 -a 2 f1 f2`
`join -v 1 A B`	Only unmatched from A	`join -v 1 f1 f2`
`join -t ',' A B`	Custom delimiter	`join -t ',' f1.csv f2.csv`
`join -i A B`	Case-insensitive	`join -i f1 f2`
`join -1 N -2 M A B`	Join on different fields	`join -1 2 -2 2 f1 f2`
`join -o FMT A B`	Custom output	`join -o 1.1,1.2,2.2 f1 f2`
`join -e STR -a 1 A B`	Fill missing fields	`join -e N/A -a 1 f1 f2`

Key takeaways:

cut extracts fields (-f) or characters (-c) from each line
Use -d to set the delimiter — default is TAB, not space
cut requires single-character delimiters — for multi-char, use awk -F
paste merges files side by side, TAB-separated by default
Use paste -d to choose a delimiter — perfect for building CSVs
Use paste -s to collapse a file into a single line
join combines two files on a shared key — like SQL’s JOIN
Always sort both files on the join key before joining
Use -a N to include unmatched lines, -v N for only unmatched
Use -t for a custom delimiter, -i for case-insensitive matching
Use -o to control the output fields and -e to fill in missing values
Combine all three with process substitution for powerful pipelines

Remember: cut is vertical — it slices columns. paste is horizontal — it stitches files together. join is relational — it matches rows. All three assume structured text, so know your delimiters. cut breaks on multi-char delimiters and quoted CSV fields — reach for awk when you need more power. join needs sorted input, just like uniq. And paste is your go-to for turning separate columns into a CSV. Master these three, and you can reshape tabular text without ever opening a spreadsheet.

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a – cut command

b – paste command

c – join command

Complete Example Session

Quick Reference

cut

paste

join

Tool Comparison

Best Practices

Common Pitfalls

Real-World Examples

1. Extract Usernames from /etc/passwd

2. Extract Username and UID

3. Build a CSV from Two Columns

4. Add Line Numbers to a File

5. Convert a Column into a Single Line

6. Join Users with Their Scores

7. Show Users Without Scores

8. Full Outer Join

9. Join with a Different Delimiter

10. Extract Fixed-Width Columns

11. Merge Multiple Files Side by Side

12. Join and Format Output

13. Filter Columns and Reorder

14. Combine cut + sort + uniq

15. Build a Report from /etc/passwd

Visual: cut vs paste vs join

Summary

Ads Blocker Detected!!!

1. Extract Usernames from `/etc/passwd`

15. Build a Report from `/etc/passwd`