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问题
当我们在linux shell(如bash)中使用管道执行多个命令时,$?
只能获取到最后一条命令的返回码,那么应该怎么获取管道前面的命令的返回码呢,请看下文:
当执行一条管道命令时,linux会使用PIPESTATUS这个数组变量来保存每个管道的返回码。PIPESTATUS[0]
表示管道中第一个命令的返回码,PIPESTATUS[1]
表示第二个命令的返回值,这是一个共享的变量,为避免别的命令改变它的内容,可以将它复制到一个新的数组。
#!/bin/bash echo "tftf" true | false | true | false RC=( "${PIPESTATUS[@]}" ) echo "RC[0] = ${RC[0]}" # true = 0 echo "RC[1] = ${RC[1]}" # false = 1 echo "RC[2] = ${RC[2]}" # true = 0 echo "RC[3] = ${RC[3]}" # false = 1 echo "ftft" false | true | false | true RC=( "${PIPESTATUS[@]}" ) echo "RC[0] = ${RC[0]}" # false = 1 echo "RC[1] = ${RC[1]}" # true = 0 echo "RC[2] = ${RC[2]}" # false = 1 echo "RC[3] = ${RC[3]}" # true = 0 echo "fftt" false | false | true | true RC=( "${PIPESTATUS[@]}" ) echo "RC[0] = ${RC[0]}" # false = 1 echo "RC[1] = ${RC[1]}" # false = 1 echo "RC[2] = ${RC[2]}" # true = 0 echo "RC[3] = ${RC[3]}" # true = 0
执行上面的bash文件,输出如下所示:
jagitch@jagitch-MS-7B93:~$ source pipeline.sh tftf RC[0] = 0 RC[1] = 1 RC[2] = 0 RC[3] = 1 ftft RC[0] = 1 RC[1] = 0 RC[2] = 1 RC[3] = 0 fftt RC[0] = 1 RC[1] = 1 RC[2] = 0 RC[3] = 0
一个具体的实例
#!/bin/bash WEB_SERVER=steve-parker.org curl -# -f -u ${USERNAME}:${PASSWORD} http://${WEB_SERVER}/ | grep "SomeMessage" RC=( "${PIPESTATUS[@]}" ) if [ "${RC[0]}" -eq "22" ]; then # curl returned 22, indicating some error above 400, # such as: 404 Not Found, 401 Unauthorized, etc. echo "Invalid credentials" exit 1 fi # PIPESTATUS has gone, but we can still inspect RC if [ "${RC[1]}" -eq "0" ]; then echo "Grep succeeded" echo "Web server reported SomeMessage" else echo "Web server didn't report SomeMessage" fi
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