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| -rw-r--r-- | src/tools/awk.md | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/src/tools/awk.md b/src/tools/awk.md index 96212d5..a0c2470 100644 --- a/src/tools/awk.md +++ b/src/tools/awk.md @@ -45,6 +45,11 @@ fields ----> run associated action Any valid awk `expr` can be a `pattern`. +An example is the regex pattern `/abc/ { print $1 }` which prints the first +field if the record matches the regex `/abc/`. This form is actually a short +version for `$0 ~ /abc/ { print $1 }`, see the regex comparison operator +below. + ### Special pattern awk provides two special patterns, `BEGIN` and `END`, which can be used @@ -92,6 +97,15 @@ multiple times. Actions with those patterns are **executed exactly once**. - `%S` second (00-59) - `%T` alias for `%H:%M:%S` +- `S ~ R`, `S !~ R` + + The regex comparison operator, where the former returns true if the string + `S` matches the regex `R`, and the latter is the negated form. + The regex can be either a + [constant](https://www.gnu.org/software/gawk/manual/html_node/Regexp-Usage.html) + or [dynamic]( + https://www.gnu.org/software/gawk/manual/html_node/Computed-Regexps.html) + regex. ## Examples @@ -110,7 +124,8 @@ Matches records not starting with `#`. ### Range patterns ```bash -echo -e "a\nFOO\nb\nc\nBAR\nd" | awk '/FOO/,/BAR/ { print }' +echo -e "a\nFOO\nb\nc\nBAR\nd" | \ + awk '/FOO/,/BAR/ { print }' ``` `/FOO/,/BAR/` define a range pattern of `begin_pattern, end_pattern`. When `begin_pattern` is matched the range is **turned on** and when the @@ -120,7 +135,7 @@ in the range _inclusive_. An _exclusive_ range must be handled explicitly, for example as follows. ```bash echo -e "a\nFOO\nb\nc\nBAR\nd" | \ - awk '/FOO/,/BAR/ { if (!($1 ~ "FOO") && !($1 ~ "BAR")) { print } }' + awk '/FOO/,/BAR/ { if (!($1 ~ "FOO") && !($1 ~ "BAR")) { print } }' ``` ### Access last fields in records |