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「服務」帶來意想不到的結果grep`

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「服務」帶來意想不到的結果grep` 
$ sudo service --status-all | fgrep -e 'bluetooth'
 [ ? ]  alsa-utils
 [ ? ]  binfmt-support
 [ + ]  bluetooth
 [ ? ]  cpufrequtils
 [ ? ]  cryptdisks
 [ ? ]  cryptdisks-early
 [ ? ]  hdparm
 [ ? ]  hwclock.sh
 [ ? ]  kmod
 [ ? ]  loadcpufreq
 [ ? ]  networking
 [ ? ]  plymouth
 [ ? ]  plymouth-log
 [ ? ]  pppd-dns
 [ ? ]  udev-finish
 [ ? ]  virtualbox-guest-x11
$ sudo service bluetooth stop
[ ok ] Stopping bluetooth: /usr/sbin/bluetoothd.
$ sudo service --status-all | fgrep -e 'bluetooth'
 [ ? ]  alsa-utils
 [ ? ]  binfmt-support
 [ - ]  bluetooth
 [ ? ]  cpufrequtils
 [ ? ]  cryptdisks
 [ ? ]  cryptdisks-early
 [ ? ]  hdparm
 [ ? ]  hwclock.sh
 [ ? ]  kmod
 [ ? ]  loadcpufreq
 [ ? ]  networking
 [ ? ]  plymouth
 [ ? ]  plymouth-log
 [ ? ]  pppd-dns
 [ ? ]  udev-finish
 [ ? ]  virtualbox-guest-x11

service | grep當只有 1 行（在每個輸出集中）與模式相符時，為什麼我會得到多於 1 行的輸出行grep？開頭的幾行有什麼（不好的）魔力嗎[?]？或者，我錯過了什麼？

FWIW，我正在跑步

$ date
Tue Nov 28 20:51:46 MST 2017
$ uname -rsv
Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2+deb8u5 (2017-09-19)
$ lsb_release -ds
LMDE 2 Betsy
$ cat /etc/debian_version
8.9
$ gcc --version | head -n 1
gcc (Debian 4.9.2-10) 4.9.2

答案1

在我看來@Sundeep 是對的。

如果您查看腳本是否service存在導致此行為的重新導向

if ! is_ignored_file "${SERVICE}" \
    && [ -x "${SERVICEDIR}/${SERVICE}" ]; then
    out=$(env -i LANG="$LANG" LANGUAGE="$LANGUAGE" LC_CTYPE="$LC_CTYPE" LC_NUMERIC="$LC_NUMERIC" LC_TIME="$LC_TIME" LC_COLLATE="$LC_COLLATE" LC_MONETARY="$LC_MONETARY" LC_MESSAGES="$LC_MESSAGES" LC_PAPER="$LC_PAPER" LC_NAME="$LC_NAME" LC_ADDRESS="$LC_ADDRESS" LC_TELEPHONE="$LC_TELEPHONE" LC_MEASUREMENT="$LC_MEASUREMENT" LC_IDENTIFICATION="$LC_IDENTIFICATION" LC_ALL="$LC_ALL" PATH="$PATH" TERM="$TERM" "$SERVICEDIR/$SERVICE" status 2>&1)
    retval=$?
    if echo "$out" | egrep -iq "usage:"; then
        #printf " %s %-60s %s\n" "[?]" "$SERVICE:" "unknown" 1>&2
        echo " [ ? ]  $SERVICE" 1>&2          #<-------------------HERE
        continue
    else
    if [ "$retval" = "0" -a -n "$out" ]; then
        #printf " %s %-60s %s\n" "[+]" "$SERVICE:" "running"
        echo " [ + ]  $SERVICE"
        continue
    else
        #printf " %s %-60s %s\n" "[-]" "$SERVICE:" "NOT running"
        echo " [ - ]  $SERVICE"
        continue
    fi
fi

重定向是針對錯誤情況的（服務不支援呼叫status），因此雖然可見輸出是[ ? ]“juju”，但實際上是繞過 grep 的重定向。

在命令列上測試這個......

~$ echo "banana" | grep bluetooth       #nothing echoed
~$ echo "banana" 1>&2 | grep bluetooth  #bingo, get a banana
banana

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