得到command的退出状态_退出command

shell脚本执行的每个命令都会有退出状态，退出状态是一个数值，0表示命令执行成功，非0表示命令执行失败。
通过$?得到上一个执行命令的退出状态。

date
echo $?
date-foo-bar
printf '%d\n' $?
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得到命令的退出状态

command
status=$?
## run date command ##
cmd="date"
$cmd
## get status ##
status=$?
## take some decision ## 
[ $status -eq 0 ] && echo "$cmd command was successful" || echo "$cmd failed"
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#!/bin/bash
#
# Sample shell script to demo exit code usage #
#
set -e
 
## find ip in the file ##
grep -q 192.168.2.254 /etc/resolv.conf
 
## Did we found IP address? Use exit status of the grep command ##
if [ $? -eq 0 ]
then
  echo "Success: I found IP address in file."
  exit 0
else
  echo "Failure: I did not found IP address in file. Script failed" >&2
  exit 1
fi
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