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Linux bash unset environment variable


How to Set and Unset Local, User and System Wide

This form is to remove the described pattern trying to match it from the beginning of the string. Look at the following examples to get the idea (matched text marked striked, remember it will be removed. The operator “#” will try to remove the shortest text matching the pattern, while “##” tries to do it with the longest text matching.

And deleting an environment variable in bash:. Tagged linux environment-variables unset or ask. How do I delete an exported environment variable.

I’m currently writing a bash testing framework, where in a test function, both standard bash tests ([[) as well as predefined matchers can be used. Matchers are wrappers to ‘[[‘ and besides returning a return code, set some meaningful message saying what was expected.

Exec bash command cleared all the local variables but not environment variables. Unset all environment variables back to default on login: [email protected]:~$ export DOGE="so wow" [email protected]:~$ env | grep DOGE DOGE=so wow [email protected]:~$ env -i bash [email protected]:~$ env | grep DOGE [email protected]:~$.

For example, the "LANG" environment variable determines the language in. Environment variables provide a way to influence the behaviour of software on the system.

[email protected]} => testone testtwo testthree echo “${. [email protected]}” => testone testtwo testthree. Test*}” => testone:testtwo:testthree echo ${. Testone=; testtwo=; testthree=; IFS=”:”; echo “${. Test*} => testone testtwo testthree echo ${.

During the installation, something went wrong. Before installing gnuplot, I set the environment variable GNUPLOT_DRIVER_DIR = /home/gnuplot/build/src.

SHELL /bin/bash The user’s preferred command-line shell as it is set in the /etc/passwd file. TERM xterm The name of a terminal information file from /lib/terminfo, this file instructs terminal programs how to achieve things such as displaying color. LINES 25 The number of text lines on the console window. TERMCAP This variable can be used instead of “TERM” to manually specify terminal information rather than point to a file. SDL_VIDEO_FULLSCREEN_DISPLAY 0 In multiple monitor setups, such as Xinerama or TwinView, this sets which screen to use for full-screen mode for SDL applications/games. TZ IST-2
:Japan This variable was used by older UNIX systems to specify the system’s time-zone. This variable is set by the system. HOME /home/myuser1 The location of the currently logged-in user’s home directory. This typically makes various GNU extensions that make life easier not work, but it may just be what’s needed to make an old UNIX script execute successfully. The value of this variable can either be the name and offset of a time-zone (as seen in the first example) or the name of a zone-info file in /usr/share/zoneinfo (as seen in the second example). This variable can, however, be used to make one user’s particular session display times in a different time-zone than the rest of the system. Try adjusting this variable if lines don’t seem to wrap properly in the console. PWD /home/myuser1/Desktop The current working directory of the shell. However, Ubuntu and most other modern systems use the /etc/localtime file for that purpose. You probably shouldn’t change its value manually. POSIXLY_CORRECT N/A If this environment variable exists, regardless of its value, it causes the behaviour of quite a few utilities to more closely match the behaviour defined by the POSIX standard. It may help to fiddle with this variable if you’re trying use an odd terminal emulator program or trying to connect a hardware serial-port terminal emulator and getting undesired results. LOGNAME myuser1 Similar to “USER”, some programs prefer to read this variable rather than USER. COLUMNS 80 The number of text columns in the terminal window. This typically does not need to be set manually, as the system searches for such files in /usr/share/zoneinfo by default. Other environment variables Variable Value Examples What it’s for USER myuser1 The name of the currently logged-in user. If unset all screens are used. Try adjusting this variable if you’re getting strange results when scrolling text. TZDIR /usr/share/zoneinfo The path of the directory containing time-zone information files. Aliases The name of a file containing host-name aliases for use with various network programs.

PWD command is a very common system variable which is used to store the present working directory. The whole concept of setting and un-setting environment variables revolves around some set of files and few commands and different shells. User defined variables are typically set by user, either temporarily for the current shell or permanently.

Declare tText=”ABCDEFG” declare tFind=”CD” declare tTemp=${tText/”$tFind”/} # $tFind present in $tText. Declare -i tFPos # Calculate $tFind position if test “$Text”. = “$tTemp” ; then echo “Found $tFind in $tText” fi tTemp=${tText#*”$tFind”} # “EFG” (Out of original 7 characters, 3 remain so 7-3=4 were removed) tFPos=${#tText}-${#tTemp}-${#tFind} # 7-3-2=2 (Out of 4 removed, $tFind accounts for 2, so 2 precede $tFind) echo “Found $tFind at position $tFPos” # 2.

#### # Example cases for unset/empty arrays and nullstring elements #### ### CASE 1: Unset array (no array) # make sure we have no array at all unset array echo ${array[@]:-This array is NULL or unset} echo ${array[@]-This array is NULL or unset} ### CASE 2: Set but empty array (no elements) # declare an empty array array=() echo ${array[@]:-This array is NULL or unset} echo ${array[@]-This array is NULL or unset} ### CASE 3: An array with only one element, a nullstring array=(“”) echo ${array[@]:-This array is NULL or unset} echo ${array[@]-This array is NULL or unset} ### CASE 4: An array with only two elements, a nullstring and a normal word array=(“” word) echo ${array[@]:-This array is NULL or unset} echo ${array[@]-This array is NULL or unset}.

When a parent process creates a child process, for example when we run the “gedit” command from the terminal and “bash” (the parent process) creates “gedit” (the child process), the child process inherits all the environment variables and values the parent process had.


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