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| -rw-r--r-- | _notes/bash.md | 135 |
1 files changed, 79 insertions, 56 deletions
diff --git a/_notes/bash.md b/_notes/bash.md index 6529b59..1feef07 100644 --- a/_notes/bash.md +++ b/_notes/bash.md @@ -10,17 +10,20 @@ subtitle: best practices `"${#xs[@]}"` doesn't work with `nounset` if `xs` wasn't defined, i.e. was declared with either of - local -a xs - declare -a xs - local -A xs - declare -A xs +```bash +local -a xs +declare -a xs +local -A xs +declare -A xs +``` Therefore, if you want to extract the length of an array, append `=()` to the statements above. - local -a xs=() - declare -a xs=() - ... +```bash +local -a xs=() +declare -a xs=() +``` And now `"${#xs[@]}"` works with `nounset`. It doesn't affect expansion (see below) though. @@ -29,29 +32,37 @@ It doesn't affect expansion (see below) though. #### Do - func ${arr[@]+"${arr[@]}"} +```bash +func ${arr[@]+"${arr[@]}"} +``` #### Don't - func "${arr[@]}" # Doesn't work with `nounset`. - func "${arr[@]+"${arr[@]}"}" # Doesn't work properly with `declare -a arr=('')`. +```bash +func "${arr[@]}" # Doesn't work with `nounset`. +func "${arr[@]+"${arr[@]}"}" # Doesn't work properly with `declare -a arr=('')`. +``` ### `unset` #### Do - unset -v 'arr[x]' - unset -v 'arr[$i]' +```bash +unset -v 'arr[x]' +unset -v 'arr[$i]' +``` #### Don't - unset -v arr[x] # May break due to globbing. - unset -v arr[$i] # The same as above + a possible problem with quotation. - unset -v 'arr["x"]' # Doesn't work for some reason. - unset -v 'arr["]"]' # The same as above; just highlighting the problem with funny characters in array indices. - unset -v 'arr["$i"]' # Also rejected. +```bash +unset -v arr[x] # May break due to globbing. +unset -v arr[$i] # The same as above + a possible problem with quotation. +unset -v 'arr["x"]' # Doesn't work for some reason. +unset -v 'arr["]"]' # The same as above; just highlighting the problem with funny characters in array indices. +unset -v 'arr["$i"]' # Also rejected. - # An insightful discussion on the topic: https://lists.gnu.org/archive/html/help-bash/2016-09/msg00020.html. +# An insightful discussion on the topic: https://lists.gnu.org/archive/html/help-bash/2016-09/msg00020.html. +``` `errexit` --------- @@ -63,67 +74,79 @@ useful behaviour. #### Do - shopt -s inherit_errexit # Without this, bar will be executed w/ errexit disabled! +```bash +shopt -s inherit_errexit # Without this, bar will be executed w/ errexit disabled! - bar() { - false - echo 'should never see this' >&2 - } +bar() { + false + echo 'should never see this' >&2 +} - bar_output="$( bar )" - foo "$bar_output" +bar_output="$( bar )" +foo "$bar_output" +``` #### Don't - bar() { - false - echo 'should never see this' >&2 - } +```bash +bar() { + false + echo 'should never see this' >&2 +} - foo "$( bar )" # Even with errexit, foo will still get executed. - # More than that, the script will print 'should never see this'! +foo "$( bar )" # Even with errexit, foo will still get executed. + # More than that, the script will print 'should never see this'! +``` ### Process substitution #### Do - output="$( command )" +```bash +output="$( command )" - while IFS= read -r line; do - process_line "$line" - done <<< "$output" +while IFS= read -r line; do + process_line "$line" +done <<< "$output" +``` #### Don't - # This causes some bash insanity where you cannot change directories or set - # variables inside a loop: http://mywiki.wooledge.org/BashFAQ/024 - command | while IFS= read -r line; do - process_line "$line" - done +```bash +# This causes some bash insanity where you cannot change directories or set +# variables inside a loop: http://mywiki.wooledge.org/BashFAQ/024 +command | while IFS= read -r line; do + process_line "$line" +done - # errexit doesn't work here no matter what: - while IFS= read -r line; do - process_line "$line" - done < <( command ) - echo 'should never see this' +# errexit doesn't work here no matter what: +while IFS= read -r line; do + process_line "$line" +done < <( command ) +echo 'should never see this' +``` ### Functions #### Do - foo() { - false - echo 'should never see this' >&2 - } +```bash +foo() { + false + echo 'should never see this' >&2 +} - foo - echo ok +foo +echo ok +``` #### Don't - if foo; then - echo ok # foo will still print 'should never see this'. - fi +```bash +if foo; then + echo ok # foo will still print 'should never see this'. +fi - foo && echo ok # Same here. - foo || echo ok +foo && echo ok # Same here. +foo || echo ok +``` |