Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
restores the original $PATH (a child process, such as a script, may not change the environment of the
parent process, the shell).
The current "working directory", ./, is usually omitted from the $PATH as a security
measure.
$PIPESTATUS
Exit status of last executed foreground pipe. Interestingly enough, this does not give the same result
as the exit status of the last executed command.
bash$ echo $PIPESTATUS
0
bash$ ls −al | bogus_command
bash: bogus_command: command not found
bash$ echo $PIPESTATUS
141
bash$ ls −al | bogus_command
bash: bogus_command: command not found
bash$ echo $?
127
The $PIPESTATUS variable may contain an erroneous 0 value in a login shell.
tcsh% bash
bash$ who | grep nobody | sort
bash$ echo ${PIPESTATUS[*]}
0
The above lines contained in a script would produce the expected 0 1 0 output.
$PPID
Thank you, Wayne Pollock for pointing this out and supplying the above example.
The $PPID of a process is the process id (pid) of its parent process. [19]
$PS1
$PS2
$PS3
$PS4
$PWD
Compare this with the pidof command.
This is the main prompt, seen at the command line.
The secondary prompt, seen when additional input is expected. It displays as ">".
The tertiary prompt, displayed in a select loop (see Example 10−29).
The quartenary prompt, shown at the beginning of each line of output when invoking a script with the
−x option. It displays as "+".
working directory (directory you are in at the time)
This is the analog to the pwd builtin command.
Chapter 9. Variables Revisited 68