cut and tr

cut — slice columns

cut picks fields out of structured input. Three modes:

cut -f 2 — second tab-separated field.
cut -d ',' -f 1,3 — first and third comma-separated.
cut -c 1-10 — first 10 characters of each line.
cut -d ' ' -f 2- — from field 2 to end.

Useful on CSV, TSV, and any line-oriented log with a fixed delimiter. For complex parsing prefer awk (next track).

tr — translate or delete characters

tr reads stdin character by character and translates. Two main forms:

tr 'a-z' 'A-Z' — uppercase.
tr -d ' ' — delete spaces.
tr -s ' ' — squeeze runs of spaces into one.
tr -c 'a-zA-Z0-9' '_' — replace anything not alphanumeric with _ (complement).

Real-world combos

Get unique IPs from a log: cut -d ' ' -f 1 access.log | sort -u
Lowercase a file: tr 'A-Z' 'a-z' < INPUT > output
Strip Windows line endings: tr -d '\r' < in.txt > out.txt
Replace tabs with spaces: tr '\t' ' '

Limits of cut

cut can't handle quoted CSV (commas inside quotes). For real CSV use csvkit, miller, or Python's csv module. cut is fine for simple delimited logs.

Code

Pull users from /etc/passwd·bash

cut -d ':' -f 1 /etc/passwd | head
# With shell
cut -d ':' -f 1,7 /etc/passwd | head

Normalize a name field·bash

echo '  John   Doe' \
  | tr -s ' '            \  # collapse whitespace
  | tr 'A-Z' 'a-z'       \  # lowercase
  | sed 's/^ //'         \  # leading space
  | tr ' ' '-'              # space -> dash

cut — slice columns

tr — translate or delete characters

Real-world combos

Limits of cut

Code

External links

Exercise

Progress

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