问题
I am new with unix and I am writing a shell script.
When I run this line on the command prompt, it prints the total count of the number of processes which matches:
ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'
example, the output of the above line is 2 in the command prompt.
I want to write a shell script in which the output of the above line (2) is assigned to a variable, which will be later be used for comparison in an if statement.
I am looking for something like
output= `ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'`
echo $output
But when i run it, it says output could not be found whereas I am expecting 2. Please help.
回答1:
You can use a $ sign like:
OUTPUT=$(expression)
回答2:
Try:
output=$(ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'); echo $output
Wrapping your command in $( ) tells the shell to run that command, instead of attempting to set the command itself to the variable named "output". (Note that you could also use backticks `command`.)
I can highly recommend http://tldp.org/LDP/abs/html/commandsub.html to learn more about command substitution.
Also, as 1_CR correctly points out in a comment, the extra space between the equals sign and the assignment is causing it to fail. Here is a simple example on my machine of the behavior you are experiencing:
jed@MBP:~$ foo=$(ps -ef |head -1);echo $foo
UID PID PPID C STIME TTY TIME CMD
jed@MBP:~$ foo= $(ps -ef |head -1);echo $foo
-bash: UID: command not found
UID PID PPID C STIME TTY TIME CMD
回答3:
If you want to do it with multiline/multiple command/s then you can do this:
output=$( bash <<EOF
#multiline/multiple command/s
EOF
)
Or:
output=$(
#multiline/multiple command/s
)
Example:
#!/bin/bash
output="$( bash <<EOF
echo first
echo second
echo third
EOF
)"
echo "$output"
Output:
first
second
third
来源：https://stackoverflow.com/questions/20688552/assigning-the-output-of-a-command-to-a-variable