5 ms·

Sometimes you just want some 30-50 lines of piping a few commands and a couple of conditionals. Python (the language with the most community traction to replac

Sometimes you just want some 30-50 lines of piping a few commands and a couple of conditionals. Python (the language with the most community traction to replace bash for scripts) is a royal pain to use for this without libraries that are present in no default system, and even with those it often ends up being more verbose than it should.

nisa 8y ago
> Sometimes you just want some 30-50 lines of piping a few commands and a couple of conditionals. maybe I was not clear - nothing against shell-scripting but doing some weird dancing like in the article is imho useless, also depending on bash is a stupid idea imho. posix sh + shellcheck is all you need. if you can't solve your problem in posix sh rethink your code / approach and simplify until it will work.
- deleted 8y ago
  [deleted]
- thisacctforreal 8y ago
  I agree. I've used this page successfully as reference for portable syntax: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3... Some sections on features I use heavily: - Parameter Expansion (specifically :-, %, %%, #, ##) - Special Parameters (specifically "$@", $#, $?) - set --, this lets you set the $1, $2, etc. variables. I use this with "$@" for arrays, primarily for building command strings. Here's an small shell script demonstrating some of them: #!/bin/sh # err function err() { echo "$1" >&2; exit 1; } # init variables unset src unset dst dry_run=false # get arguments while [ $# -gt 0 ]; do case "$1" in -d|--dry-run) dry_run=true ;; --) shift; break ;; -*) err "unknown option: $1" ;; *) if [ -z "$src" ]; then src="$1" elif [ -z "$dst" ]; then dst="$1" else err "unexpected argument: $1" fi ;; esac shift done # sanity checks ## TODO: print usage if [ -z "$src" ]; then err "source not specified"; fi if [ ! -d "$src" ]; then err "source does not exist"; fi if [ ! -r "$src" ]; then err "cannot read source directory"; fi if [ -z "$dst" ]; then err "destination not specified"; fi if ! rsync --version >/dev/null 2>&1; then err "missing rsync(1)" fi # build rsync command set -- rsync -aq "$src" "$dst" # log command echo "copying $src to $dst" echo " $@" if ! $dry_run; then if "$@"; then echo "success" else # rsync will have printed an error message err "rsync exited with error code $?" fi else echo "dry run; not executing" fi Also be sure to read the man page for test (the [ command).
user5994461 8y ago
For typical system scripts, ansible is much better than bash. It has all the commands that are missing from Unix and it's not subject to the bash problems mentioned here. I agree that python is a pain. It's too low level for any task.

nisa 8y ago

> Sometimes you just want some 30-50 lines of piping a few commands and a couple of conditionals. maybe I was not clear - nothing against shell-scripting but doing some weird dancing like in the article is imho useless, also depending on bash is a stupid idea imho. posix sh + shellcheck is all you need. if you can't solve your problem in posix sh rethink your code / approach and simplify until it will work.

deleted 8y ago
[deleted]
thisacctforreal 8y ago
I agree. I've used this page successfully as reference for portable syntax: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3... Some sections on features I use heavily: - Parameter Expansion (specifically :-, %, %%, #, ##) - Special Parameters (specifically "$@", $#, $?) - set --, this lets you set the $1, $2, etc. variables. I use this with "$@" for arrays, primarily for building command strings. Here's an small shell script demonstrating some of them: #!/bin/sh # err function err() { echo "$1" >&2; exit 1; } # init variables unset src unset dst dry_run=false # get arguments while [ $# -gt 0 ]; do case "$1" in -d|--dry-run) dry_run=true ;; --) shift; break ;; -*) err "unknown option: $1" ;; *) if [ -z "$src" ]; then src="$1" elif [ -z "$dst" ]; then dst="$1" else err "unexpected argument: $1" fi ;; esac shift done # sanity checks ## TODO: print usage if [ -z "$src" ]; then err "source not specified"; fi if [ ! -d "$src" ]; then err "source does not exist"; fi if [ ! -r "$src" ]; then err "cannot read source directory"; fi if [ -z "$dst" ]; then err "destination not specified"; fi if ! rsync --version >/dev/null 2>&1; then err "missing rsync(1)" fi # build rsync command set -- rsync -aq "$src" "$dst" # log command echo "copying $src to $dst" echo " $@" if ! $dry_run; then if "$@"; then echo "success" else # rsync will have printed an error message err "rsync exited with error code $?" fi else echo "dry run; not executing" fi Also be sure to read the man page for test (the [ command).

user5994461 8y ago

For typical system scripts, ansible is much better than bash. It has all the commands that are missing from Unix and it's not subject to the bash problems mentioned here. I agree that python is a pain. It's too low level for any task.