cut, paste & join — Column Tools#

cut#

Extract specific fields or byte/character ranges from each line.

Syntax#

cut OPTION... [FILE...]

By delimiter field (-d / -f)#

cut -d: -f1           /etc/passwd    # first field (username)
cut -d: -f1,7         /etc/passwd    # fields 1 and 7
cut -d: -f1-3         /etc/passwd    # fields 1 through 3
cut -d: -f3-          /etc/passwd    # field 3 to end
cut -d, -f2           data.csv       # CSV second column
cut -d$'\t' -f1,3     data.tsv       # tab-delimited fields 1 and 3
cut -d' ' -f2-        sentence.txt   # all words except first

# Change output delimiter (cut has no -D; use tr or awk)
cut -d: -f1,3 /etc/passwd | tr ':' '\t'

By character position (-c)#

cut -c1       file.txt    # first character of each line
cut -c1-10    file.txt    # characters 1–10
cut -c5-      file.txt    # character 5 to end
cut -c1,5,10  file.txt    # characters 1, 5, and 10
cut -c-80     file.txt    # max 80 chars (truncate long lines)

By byte position (-b)#

cut -b1-4   binary.dat   # bytes 1–4 (differs from -c for multibyte chars)

Suppress undelimited lines#

cut -d: -f1 -s /etc/passwd   # -s: skip lines without the delimiter

paste#

Merge files horizontally (column-by-column).

Syntax#

paste [OPTIONS] [FILE...]

paste file1.txt file2.txt            # merge side by side (tab-delimited)
paste -d, file1.txt file2.txt        # use comma as delimiter
paste -d'\t' names.txt emails.txt    # explicit tab

# Serial mode (-s): transpose — each file becomes one tab-joined line
paste -s file.txt
paste -s -d, file.txt                # comma-separated

# Combine N columns from same file
paste - - < file.txt             # 2 lines → 1 row (2 columns)
paste - - - < file.txt           # 3 lines → 1 row (3 columns)

Practical paste examples#

# Create a CSV from two column files
paste -d, ids.txt names.txt > combined.csv

# Add line numbers to a file
seq 1 $(wc -l < file.txt) | paste -d'\t' - file.txt

# Interleave lines from two files
paste -d'\n' file1.txt file2.txt

# Recreate a CSV from a column of values
paste -s -d, values.txt

join#

Join lines from two files on a common key field (like SQL inner join).

Syntax#

join [OPTIONS] FILE1 FILE2

Both files must be sorted on the join key first.

# Join on field 1 (default)
join sorted1.txt sorted2.txt

# Join on specific fields
join -1 2 -2 1 file1.txt file2.txt   # field 2 of f1, field 1 of f2

# Change output delimiter
join -t, file1.csv file2.csv

# Include unmatched lines (outer join)
join -a 1 file1.txt file2.txt        # + unmatched from file1
join -a 2 file1.txt file2.txt        # + unmatched from file2
join -a 1 -a 2 file1.txt file2.txt   # full outer join

# Fill missing fields
join -a 1 -e 'N/A' -o 0,1.2,2.2 file1.txt file2.txt

# Suppress matched lines (anti-join)
join -v 1 file1.txt file2.txt    # lines in f1 not in f2
join -v 2 file1.txt file2.txt    # lines in f2 not in f1

join example#

# employees.txt (sorted by ID):
# 101 Alice
# 102 Bob
# 103 Carol

# salaries.txt (sorted by ID):
# 101 75000
# 102 82000
# 104 91000

join employees.txt salaries.txt
# 101 Alice 75000
# 102 Bob 82000

join -a 1 employees.txt salaries.txt
# 101 Alice 75000
# 102 Bob 82000
# 103 Carol           ← Carol has no salary record

Practical pipelines#

# Extract second column from CSV, remove header, sort, count unique
tail -n +2 data.csv | cut -d, -f2 | sort | uniq -c | sort -rn

# Get all usernames from /etc/passwd
cut -d: -f1 /etc/passwd | sort

# Get the home directories of users with /bin/bash shell
grep '/bin/bash$' /etc/passwd | cut -d: -f6

# Compare two lists (IDs in file1 not in file2)
join -v 1 <(sort ids1.txt) <(sort ids2.txt)

# Build a quick lookup from key=value file
cut -d= -f1,2 config.env | tr '=' '\t'

# Transpose a whitespace-delimited matrix
# (for small matrices — use awk for larger ones)
paste $(for i in $(seq 1 $(awk '{print NF; exit}' matrix.txt)); do
  echo <(cut -d' ' -f$i matrix.txt)
done)

[!TIP] cut always outputs fields in the order they appear in the input, regardless of the order specified with -f. To reorder fields, use awk '{print $3, $1}' instead.

[!TIP] join requires sorted input. Use join <(sort f1) <(sort f2) or pre-sort with sort -k1 when sorting on a non-first field.