mirror of https://github.com/CrimsonTome/tldr.git
common/*: update pages of POSIX special Built-In utilities (#11858)
* eval, exec, exit, export, readonly, set, shift, trap: use Open Group links * exec, export, trap: split Linux and POSIXpull/23/head
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# eval
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# eval
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> Execute arguments as a single command in the current shell and return its result.
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> Execute arguments as a single command in the current shell and return its result.
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> More information: <https://manned.org/eval>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#eval>.
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- Call `echo` with the "foo" argument:
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- Call `echo` with the "foo" argument:
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# exec
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# exec
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> Replace the current process with another process.
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> Replace the current process with another process.
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> More information: <https://linuxcommand.org/lc3_man_pages/exech.html>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#exec>.
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- Replace with the specified command using the current environment variables:
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- Replace with the specified command using the current environment variables:
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`exec {{command -with -flags}}`
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`exec {{command -with -flags}}`
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- Replace with the specified command, clearing environment variables:
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`exec -c {{command -with -flags}}`
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- Replace with the specified command and login using the default shell:
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`exec -l {{command -with -flags}}`
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- Replace with the specified command and change the process name:
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`exec -a {{process_name}} {{command -with -flags}}`
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# exit
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# exit
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> Exit the shell.
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> Exit the shell.
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> More information: <https://manned.org/exit>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#exit>.
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- Exit the shell with the exit code of the last command executed:
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- Exit the shell with the exit code of the last command executed:
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# export
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# export
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> Command to mark shell variables in the current environment to be exported with any newly forked child processes.
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> Command to mark shell variables in the current environment to be exported with any newly forked child processes.
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> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-export>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#export>.
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- Set a new environment variable:
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- Set a new environment variable:
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`export {{VARIABLE}}={{value}}`
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`export {{VARIABLE}}={{value}}`
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- Remove an environment variable:
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`export -n {{VARIABLE}}`
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- Mark a shell function for export:
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`export -f {{FUNCTION_NAME}}`
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- Append something to the PATH variable:
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- Append something to the PATH variable:
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`export PATH=$PATH:{{path/to/append}}`
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`export PATH=$PATH:{{path/to/append}}`
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> Create or modify read-only variables within a shell script, preventing the variable from being changed by subsequent commands.
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> Create or modify read-only variables within a shell script, preventing the variable from being changed by subsequent commands.
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> This is useful when you want to ensure that a variable retains a constant value throughout the execution of a script.
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> This is useful when you want to ensure that a variable retains a constant value throughout the execution of a script.
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> More information: <https://manned.org/readonly.1p>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#readonly>.
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- Create a read-only variable:
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- Create a read-only variable:
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# set
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# set
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> Display, set or unset values of shell attributes and positional parameters.
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> Display, set or unset values of shell attributes and positional parameters.
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> More information: <https://manned.org/set>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#set>.
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- Display the names and values of shell variables:
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- Display the names and values of shell variables:
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# shift
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# shift
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> Shell built-in command that shifts the arguments passed to the calling function or script by a specified number of places.
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> Shell built-in command that shifts the arguments passed to the calling function or script by a specified number of places.
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> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-shift>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#shift>.
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- Move arguments by one place dropping the first argument:
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- Move arguments by one place dropping the first argument:
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> Automatically execute commands after receiving signals by processes or the operating system.
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> Automatically execute commands after receiving signals by processes or the operating system.
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> Can be used to perform cleanups for interruptions by the user or other actions.
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> Can be used to perform cleanups for interruptions by the user or other actions.
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> More information: <https://manned.org/trap>.
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> More information: <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap>.
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- List available signals to set traps for:
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`trap -l`
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- List active traps for the current shell:
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- List active traps for the current shell:
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`trap -p`
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`trap`
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- Set a trap to execute commands when one or more signals are detected:
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- Set a trap to execute commands when one or more signals are detected:
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# exec
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> Replace the current process with another process.
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> More information: <https://linuxcommand.org/lc3_man_pages/exech.html>.
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- Replace with the specified command using the current environment variables:
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`exec {{command -with -flags}}`
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- Replace with the specified command, clearing environment variables:
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`exec -c {{command -with -flags}}`
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- Replace with the specified command and login using the default shell:
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`exec -l {{command -with -flags}}`
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- Replace with the specified command and change the process name:
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`exec -a {{process_name}} {{command -with -flags}}`
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# export
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> Command to mark shell variables in the current environment to be exported with any newly forked child processes.
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> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-export>.
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- Set a new environment variable:
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`export {{VARIABLE}}={{value}}`
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- Remove an environment variable:
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`export -n {{VARIABLE}}`
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- Mark a shell function for export:
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`export -f {{FUNCTION_NAME}}`
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- Append something to the PATH variable:
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`export PATH=$PATH:{{path/to/append}}`
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# trap
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> Automatically execute commands after receiving signals by processes or the operating system.
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> Can be used to perform cleanups for interruptions by the user or other actions.
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> More information: <https://manned.org/trap>.
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- List available signals to set traps for:
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`trap -l`
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- List active traps for the current shell:
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`trap -p`
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- Set a trap to execute commands when one or more signals are detected:
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`trap 'echo "Caught signal {{SIGHUP}}"' {{SIGHUP}}`
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- Remove active traps:
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`trap - {{SIGHUP}} {{SIGINT}}`
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