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| Advanced Bash-Scripting Guide: | ||
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| Prev | Chapter 9. Another Look at Variables | Next |
Process ID of the current instance of Bash. This is not the same as the $$ variable, but it often gives the same result.
bash4$ echo $$ 11015 bash4$ echo $BASHPID 11015 bash4$ ps ax | grep bash4 11015 pts/2 R 0:00 bash4 |
#!/bin/bash4 echo "\$\$ outside of subshell = $$" # 9602 echo "\$BASH_SUBSHELL outside of subshell = $BASH_SUBSHELL" # 0 echo "\$BASHPID outside of subshell = $BASHPID" # 9602 echo ( echo "\$\$ inside of subshell = $$" # 9602 echo "\$BASH_SUBSHELL inside of subshell = $BASH_SUBSHELL" # 1 echo "\$BASHPID inside of subshell = $BASHPID" ) # 9603 # Note that $$ returns PID of parent process. |
An environmental variable pointing to a Bash startup file to be read when a script is invoked
A variable indicating the subshell level. This is a new addition to Bash, version 3.
See Example 21-1 for usage.
A 6-element array containing version information about the installed release of Bash. This is similar to $BASH_VERSION, below, but a bit more detailed.
# Bash version info:
for n in 0 1 2 3 4 5
do
echo "BASH_VERSINFO[$n] = ${BASH_VERSINFO[$n]}"
done
# BASH_VERSINFO[0] = 3 # Major version no.
# BASH_VERSINFO[1] = 00 # Minor version no.
# BASH_VERSINFO[2] = 14 # Patch level.
# BASH_VERSINFO[3] = 1 # Build version.
# BASH_VERSINFO[4] = release # Release status.
# BASH_VERSINFO[5] = i386-redhat-linux-gnu # Architecture
# (same as $MACHTYPE).
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$BASH_VERSION
The version of Bash installed on the system
bash$ echo $BASH_VERSION 3.2.25(1)-release |
tcsh% echo $BASH_VERSION BASH_VERSION: Undefined variable. |
Checking $BASH_VERSION is a good method of determining which shell is running. $SHELL does not necessarily give the correct answer.
A colon-separated list of search paths available to the cd command, similar in function to the $PATH variable for binaries. The $CDPATH variable may be set in the local ~/.bashrc file.
bash$ cd bash-doc bash: cd: bash-doc: No such file or directory bash$ CDPATH=/usr/share/doc bash$ cd bash-doc /usr/share/doc/bash-doc bash$ echo $PWD /usr/share/doc/bash-doc |
The top value in the directory stack [1] (affected by pushd and popd)
This builtin variable corresponds to the dirs command, however dirs shows the entire contents of the directory stack.
$EDITOR
The default editor invoked by a script, usually vi or emacs.
"effective" user ID number
Identification number of whatever identity the current user has assumed, perhaps by means of su.
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The $EUID is not necessarily the same as the $UID. |
$FUNCNAME
Name of the current function
xyz23 ()
{
echo "$FUNCNAME now executing." # xyz23 now executing.
}
xyz23
echo "FUNCNAME = $FUNCNAME" # FUNCNAME =
# Null value outside a function.
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See also Example A-50.
$GLOBIGNORE
A list of filename patterns to be excluded from matching in globbing.
Groups current user belongs to
This is a listing (array) of the group id numbers for current user, as recorded in /etc/passwd and /etc/group.
root# echo $GROUPS
0
root# echo ${GROUPS[1]}
1
root# echo ${GROUPS[5]}
6
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Home directory of the user, usually /home/username (see Example 10-7)
The hostname command assigns the system host name at bootup in an init script. However, the gethostname() function sets the Bash internal variable $HOSTNAME. See also Example 10-7.
$HOSTTYPE
host type
Like $MACHTYPE, identifies the system hardware.
bash$ echo $HOSTTYPE i686 |
internal field separator
This variable determines how Bash recognizes fields, or word boundaries, when it interprets character strings.
$IFS defaults to whitespace (space, tab, and newline), but may be changed, for example, to parse a comma-separated data file. Note that $* uses the first character held in $IFS. See Example 5-1.
bash$ echo "$IFS" (With $IFS set to default, a blank line displays.) bash$ echo "$IFS" | cat -vte ^I$ $ (Show whitespace: here a single space, ^I [horizontal tab], and newline, and display "$" at end-of-line.) bash$ bash -c 'set w x y z; IFS=":-;"; echo "$*"' w:x:y:z (Read commands from string and assign any arguments to pos params.) |
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$IFS does not handle whitespace the same as it does other characters. |