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#!/bin/bash |
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# test-shell-default-variables.sh |
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# Usage examples (you might want to `sudo apt install zsh ksh`): |
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# |
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# ./test-shell-default-variables.sh dash bash |
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# ./test-shell-default-variables.sh dash bash zsh ksh |
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# ./test-shell-default-variables.sh dash bash zsh ksh | less -R |
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# `-R` in `less -R` to have less pass escape sequences directly to the terminal |
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# so we have colors. |
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# The "when named `sh`" tests are commented because for every shell I tested |
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# (dash, bash, zsh and ksh), the output was the same as that of dash. |
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# The `test_expression` function also work with expansion changes. You can try |
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# lines like `test_expression '{BASH_SOURCE:-$0}'`. |
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echolor() { |
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echo -e "\e[1;36m$@\e[0m" |
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} |
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tell_file() { |
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echo File \`"$1"\` is: |
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echo \`\`\` |
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cat "$1" |
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echo \`\`\` |
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echo |
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} |
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SHELL_ARRAY=("$@") |
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test_command() { |
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for shell in "${SHELL_ARRAY[@]}" |
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do |
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prepare "$shell" |
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cmd="$(eval echo $1)" |
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# echo "cmd: $cmd" |
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printf '%-4s: ' "$shell" |
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{ env -i $cmd 2>&1 1>&3 | sed 's/^/[err]/'; } 3>&1 |
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teardown |
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done |
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echo |
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} |
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prepare () { |
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shell="$1" |
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PATH="$PWD/$shell/sh:$PATH" |
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} |
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teardown() { |
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PATH="${PATH#*:}" |
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} |
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### |
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### prepare |
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### |
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for shell in "${SHELL_ARRAY[@]}" |
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do |
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mkdir "$shell" |
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ln -sT "/bin/$shell" "$shell/sh" |
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done |
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echo > printer.sh |
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echo '. ./printer.sh' > sourcer.sh |
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rm linked.sh &>/dev/null; ln -sT "printer.sh" "linked.sh" |
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tell_file sourcer.sh |
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### |
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### run |
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### |
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test_expression() { |
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local expr="$1" |
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# prepare |
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echo "echo $expr" > printer.sh |
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tell_file printer.sh |
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# run |
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cmd='$shell ./printer.sh' |
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echolor "\`$cmd\` (simple invocation) ($expr):" |
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test_command "$cmd" |
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# cmd='sh ./printer.sh' |
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# echolor "\`$cmd\` (when executable name is \`sh\`) ($expr):" |
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# test_command "$cmd" |
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cmd='$shell ./sourcer.sh' |
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echolor "\`$cmd\` (via sourcing) ($expr):" |
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test_command "$cmd" |
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# cmd='sh ./sourcer.sh' |
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# echolor "\`$cmd\` (via sourcing, when name is \`sh\`) ($expr):" |
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# test_command "$cmd" |
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cmd='$shell ./linked.sh' |
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echolor "\`$cmd\` (via symlink) ($expr):" |
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test_command "$cmd" |
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# cmd='sh ./linked.sh' |
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# echolor "\`$cmd\` (via symlink, when name is \`sh\`) ($expr):" |
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# test_command "$cmd" |
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echolor "------------------------------------------" |
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echo |
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} |
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test_expression '$BASH_SOURCE' |
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test_expression '$0' |
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test_expression '$(/bin/true x y; true a b c; echo $_)' # Rq: true is a builtin |
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test_expression '$_' |
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### |
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### teardown |
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### |
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for shell in "${SHELL_ARRAY[@]}" |
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do |
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rm "$shell/sh" |
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rm -d "$shell" |
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done |
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rm sourcer.sh |
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rm linked.sh |
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rm printer.sh |
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true ' |
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# Sample output: |
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`$ ./test-shell-default-variables.sh {da,ba,z,k}sh` |
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`````` |
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File `sourcer.sh` is: |
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``` |
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. ./printer.sh |
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``` |
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File `printer.sh` is: |
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``` |
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echo $BASH_SOURCE |
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``` |
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`$shell ./printer.sh` (simple invocation) ($BASH_SOURCE): |
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dash: |
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bash: ./printer.sh |
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zsh : |
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ksh : |
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`$shell ./sourcer.sh` (via sourcing) ($BASH_SOURCE): |
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dash: |
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bash: ./printer.sh |
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zsh : |
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ksh : |
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`$shell ./linked.sh` (via symlink) ($BASH_SOURCE): |
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dash: |
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bash: ./linked.sh |
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zsh : |
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ksh : |
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------------------------------------------ |
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File `printer.sh` is: |
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``` |
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echo $0 |
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``` |
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`$shell ./printer.sh` (simple invocation) ($0): |
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dash: ./printer.sh |
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bash: ./printer.sh |
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zsh : ./printer.sh |
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ksh : ./printer.sh |
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`$shell ./sourcer.sh` (via sourcing) ($0): |
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dash: ./sourcer.sh |
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bash: ./sourcer.sh |
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zsh : ./printer.sh |
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ksh : ./sourcer.sh |
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`$shell ./linked.sh` (via symlink) ($0): |
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dash: ./linked.sh |
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bash: ./linked.sh |
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zsh : ./linked.sh |
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ksh : ./linked.sh |
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------------------------------------------ |
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File `printer.sh` is: |
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``` |
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echo $(/bin/true x y; true a b c; echo $_) |
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``` |
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`$shell ./printer.sh` (simple invocation) ($(/bin/true x y; true a b c; echo $_)): |
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dash: |
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bash: c |
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zsh : c |
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ksh : |
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`$shell ./sourcer.sh` (via sourcing) ($(/bin/true x y; true a b c; echo $_)): |
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dash: |
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bash: c |
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zsh : c |
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ksh : |
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`$shell ./linked.sh` (via symlink) ($(/bin/true x y; true a b c; echo $_)): |
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dash: |
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bash: c |
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zsh : c |
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ksh : |
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------------------------------------------ |
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File `printer.sh` is: |
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``` |
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echo $_ |
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``` |
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`$shell ./printer.sh` (simple invocation) ($_): |
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dash: |
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bash: bash |
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zsh : |
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ksh : |
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`$shell ./sourcer.sh` (via sourcing) ($_): |
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dash: |
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bash: bash |
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zsh : ./printer.sh |
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ksh : |
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`$shell ./linked.sh` (via symlink) ($_): |
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dash: |
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bash: bash |
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zsh : |
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ksh : |
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------------------------------------------ |
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`````` |
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' |
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true ' |
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# What did we learn ? |
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### `$BASH_SOURCE` |
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* `$BASH_SOURCE` works in bash and only in bash. |
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* The only difference with `$0` is when the current file was sourced by |
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another file. In that case, `$BASH_PROFILE` contains the name of the |
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sourced file, rather than that of the souring file. |
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### `$0` |
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* In zsh, `$0` has the same value as `$BASH_SOURCE` in bash. |
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### `$_` |
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* `$_` is left untouched by dash and ksh. |
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* In bash and zsh, `$_` decays to the last argument of the last call. |
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* bash initializes `$_` to "bash". |
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* zsh leaves `$_` untouched. |
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(when sourcing, it`s just the result of the "last argument" rule). |
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### Symlinks |
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* When a script is called through a symlink, no variable contains any |
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reference to the destination of the link, only its name. |
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### ksh |
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* Regarding those tests, ksh behaves like `dash`. |
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' |
