Lesson 7.2: Transforming text: cut, tr, sed and awk

Four classic filters on a server inventory: cut takes columns out, tr translates or deletes characters, sed edits lines with substitutions (and can change files in place, with a backup), awk splits lines into fields and decides what to print.

20 min

You will learn to

Cut fields out of delimited text with cut
Translate, delete and squeeze characters with tr
Substitute, print and delete lines with sed
Edit a file in place with sed -i and keep a backup
Print chosen fields and filter by a condition with awk

Key terms

Field and delimiter: Many text files are tables: each line is a record, split into fields by a delimiter such as a comma, a colon or a tab.
cut: Removes sections from each line: -d DELIM -f LIST for fields, -c LIST for character positions.
tr: Translates characters from SET1 to SET2, deletes them (-d) or squeezes repeats (-s). Reads only standard input.
sed: Stream editor: applies editing commands to each line. s/REGEX/TEXT/FLAGS substitutes, p prints, d deletes; an address (a number, a range or /pattern/) selects the lines.
awk: A pattern-action language: for each line, if the pattern matches, run the action in braces. Fields are $1, $2, ...; $0 is the whole line; NR is the line number; -F sets the field separator.
diff: Compares two files line by line: < lines exist only in the first, > only in the second.

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