Linux Shell Scripting Cookbook（Third Edition）

上QQ阅读APP看书，第一时间看更新

Getting ready

Variables are named as a sequence of letters, numbers, and underscores with no whitespace. Common conventions are to use UPPER_CASE for environment variables and camelCase or lower_case for variables used within a script.

All applications and scripts can access the environment variables. To view all the environment variables defined in your current shell, issue the env or printenv command:

$> env 
PWD=/home/clif/ShellCookBook 
HOME=/home/clif 
SHELL=/bin/bash 
# ... And many more lines

To view the environment of other processes, use the following command:

cat /proc/$PID/environ

Set PID with a process ID of the process (PID is an integer value).

Assume an application called gedit is running. We obtain the process ID of gedit with the pgrep command:

$ pgrep gedit
12501

We view the environment variables associated with the process by executing the following command:

$ cat /proc/12501/environ
GDM_KEYBOARD_LAYOUT=usGNOME_KEYRING_PID=1560USER=slynuxHOME=/home/slynux

Note that the previous output has many lines stripped for convenience. The actual output contains more variables.
The /proc/PID/environ special file contains a list of environment variables and their values. Each variable is represented as a name=value pair, separated by a null character ( \0). This is not easily human readable.

To make a human-friendly report, pipe the output of the cat command to tr, to substitute the \0 character with \n:

$ cat /proc/12501/environ  | tr '\0' '\n'