How to use a shell script to check whether a command had been installed in the Linux server All In One

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收起

How to use a shell script to check whether a command had been installed in the Linux server All In One

errors ❌

shell script error [: ：需要整数表达式
shell script error [: -eq：需要一元表达式
shell script error [: ==：需要一元表达式

#!/usr/bin/env bash

if [[ $(command -v nvm) == nvm ]]; then
  echo "❌ nvm not exist, trying to re-install it ... ⏳"
else
 echo "nvm had  been installed ✅"
fi

#!/usr/bin/env bash

temp=$(command -v nvm)
echo $temp

# if [[ $temp -eq nvm ]]; then
if [ $temp == nvm ]; then
  echo "❌ nvm not exist, trying to re-install it ... ⏳"
else
 echo "nvm had  been installed ✅"
fi

echo finished 🎉

solutions ✅

1. 如果 if 语句使用的是单层方括号 [ ] 条件修饰符, 变量必须加上双引号
2. 如果 if 语句使用的是双层方括号 [[ ]] 条件修饰符, 变量就不需要引号了

#!/usr/bin/env bash

temp=$(command -v nvm)
echo $temp

if [[ $temp == nvm ]]; then
  echo "❌ nvm not exist, trying to re-install it ... ⏳"
else
 echo "nvm had  been installed ✅"
fi

echo finished 🎉

#!/usr/bin/env bash

temp=$(command -v nvm)
echo $temp

if [ "$temp" == nvm ]; then
  echo "❌ nvm not exist, trying to re-install it ... ⏳"
else
 echo "nvm had  been installed ✅"
fi

echo finished 🎉

demos

$ cat /etc/profile
$ ls -lath /etc/profile.d

eric@rpi4b:~/Desktop $  ls -lath /etc/profile.d
总用量 44K
drwxr-xr-x 121 root root  12K  9月 21 23:42 ..
drwxr-xr-x   2 root root 4.0K  9月 21 23:35 .
-rwxr-xr-x   1 root root   81  9月 21 23:35 auto-install-test.sh
-rw-r--r--   1 root root  324  6月  8  2022 sshpwd.sh
-rw-r--r--   1 root root 1.4K  2月 18  2021 vte-2.91.sh
-rw-r--r--   1 root root  966  2月 18  2021 vte.csh
-rw-r--r--   1 root root  726  8月 12  2020 bash_completion.sh
-rw-r--r--   1 root root  450  7月 22  2019 wifi-check.sh
-rw-r--r--   1 root root   95  4月 29  2019 at-dbus-fix.sh
eric@rpi4b:~/Desktop $ cat /etc/profile
# /etc/profile: system-wide .profile file for the Bourne shell (sh(1))
# and Bourne compatible shells (bash(1), ksh(1), ash(1), ...).

if [ "$(id -u)" -eq 0 ]; then
  PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
else
  PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/games:/usr/games"
fi
export PATH

if [ "${PS1-}" ]; then
  if [ "${BASH-}" ] && [ "$BASH" != "/bin/sh" ]; then
    # The file bash.bashrc already sets the default PS1.
    # PS1='\h:\w\$ '
    if [ -f /etc/bash.bashrc ]; then
      . /etc/bash.bashrc
    fi
  else
    if [ "$(id -u)" -eq 0 ]; then
      PS1='# '
    else
      PS1='$ '
    fi
  fi
fi

if [ -d /etc/profile.d ]; then
  for i in /etc/profile.d/*.sh; do
    if [ -r $i ]; then
      . $i
    fi
  done
  unset i
fi

# profile test ✅
/home/eric/Desktop/auto-install-profile.sh
eric@rpi4b:~/Desktop $ 

/etc/profile & /etc/profile.d

boot vs login

启动配置文件加载顺序和优先级

/etc/profile
.bashrc
.zshrc
.profile
corn / corntab
systemctl service

https://www.cnblogs.com/xgqfrms/p/17343088.html

environment variables vs shell variables

全局系统环境变量 / 局部 shell 环境变量

https://www.cnblogs.com/xgqfrms/p/17686492.html

refs

https://www.cnblogs.com/xgqfrms/p/15937724.html

https://stackoverflow.com/questions/592620/how-can-i-check-if-a-program-exists-from-a-bash-script

https://www.cnblogs.com/byfboke/articles/9083853.html

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