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--- bash:shellcheck [2019/11/29 11:20] – removed peter
+++ bash:shellcheck [2020/07/15 09:30] (current) – external edit 127.0.0.1
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+====== BASH - ShellCheck ======
+[[https://github.com/koalaman/shellcheck|ShellCheck]] helps to identify a lot of potential issues in your shell scripts.
+For example, here is one common mistake which ShellCheck picks up.  Most times, the original code will work.  However if we feed $dir with value like "Denny Documents", it hurts.  Sometime the bad code may incur very severe damage!
+# Before:
+<code bash>
+rm -rf $dir
+# After:
+<code bash>
+rm -rf "$dir"
+</code>
+----
+===== More Bad Code Examples =====
+==== Common beginner's mistakes ====
+ShellCheck recognizes many common beginner's syntax errors.
+<code bash>
+var = 42                              # Spaces around = in assignments.
+$foo=42                               # $ in assignments.
+for $var in *; do ...                 # $ in for loop variables.
+var$n="Hello"                         # Wrong indirect assignment.
+echo ${var$n}                         # Wrong indirect reference.
+var=(1, 2, 3)                         # Comma separated arrays.
+</code>
+----
+==== Style ====
+ShellCheck can make recommendations to improve style:
+<code bash>
+[[ -z $(find /tmp | grep msg) ]]      # Use grep -q instead.
+a >> log; b >> log; c >> log;         # Use a redirection block instead.
+cat file | grep foo                   # Useless use of cat.
+</code>
+ShellCheck is very easy to install and use. It is built and packaged using Cabal. We can install by apt-get/yum. Or use cabal-install directly like below.
+<code bash>
+# Install ShellCheck
+sudo apt-get install -y cabal-install
+sudo cabal update
+sudo cabal install shellcheck
+ln -s /root/.cabal/bin/shellcheck /usr/sbin/shellcheck
+# Example: Run check for Shell scripts
+sudo shellcheck my_script.sh
+</code>
+By default, ShellCheck enforces hundreds of rules.  Each rule has a dedicated wiki page, which explains the purpose and improvement suggestion clearly. For example, wiki for Rule SC1000: https://github…shellcheck/wiki/SC1000.  I’m sure you can easily guess the wiki link of other rules.
+Skip some ShellCheck rules, which don’t fit your projects.  For your reference, here are rules I used to skip.
+<code bash>
+# Run test excluding certain rules
+EXCLUDE_CODE_LIST="SC1090,SC1091,SC2154,SC2001,SC2002"
+sudo shellcheck -e $EXCLUDE_CODE_LIST $file
+# Run test against all scripts under a folder
+EXCLUDE_CODE_LIST="SC1090,SC1091,SC2154,SC2001,SC2002"
+find . -name "*.sh" | xargs sudo \
+    shellcheck -e $EXCLUDE_CODE_LIST $file
+</code>
+It is recommended to enforce a daily Shell Code Check!