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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