One of the steepest Unix/Linux learning curves is the sheer number of built-in commands, all of which have many options (most of which you'll never use), and the more advanced commands are extremely complex.
To help address this, this page introduces a number of built-in Linux utilities along with some of their common options, by category.
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- Default field separators
- Tab is the default field separator for cut
- whitespace (one or more spaces or Tabs) is the default field separator for awk
- Re-ordering
- cut cannot re-order fields
- awk can re-order fields, based on the order you specify
- awk is a full-featured programming language while cut is just a single-purpose utility.
grep and regular expressions
- grep -P '<pattern>' searches for <pattern> in its input, and only outputs lines containing it
- always enclose '<pattern>' in single quotes to inhibit shell evaluation!
- pattern-matching metacharacters are very different from those in the shell
- -P says to use Perl patterns, which are much more powerful than standard grep patterns
- -v (inverse match) – only print lines with no match
- -n (line number) – prefix output with the line number of the match
- -i (case insensitive) – ignore case when matching
- -l says return only the names of files that do contain the pattern match
- -L says return only the names of files that do not contain the pattern match
- -c says just return a count of line matches
- -A <n> (After) and -B <n> (Before) – output '<n>' number of lines after or before a match
- always enclose '<pattern>' in single quotes to inhibit shell evaluation!
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