Process Management

Command Status

Branching on Success

Every command exits with a numeric status. Scripts can test that status to choose the next action.

Program

Play the script to search fixed text for a selected word and label the result.

command_status.sh 
#!/usr/bin/env bash

data=$'ok\nwarn\nfail'
needle=
if printf '%s\n' "$data" | grep -q "$needle"; then
    label="found"
else
    label="missing"
fi
echo "$needle:$label"

#!/usr/bin/env bash

data=$'ok\nwarn\nfail'
needle=
if printf '%s\n' "$data" | grep -q "$needle"; then
    label="found"
else
    label="missing"
fi
echo "$needle:$label"

#!/usr/bin/env bash

data=$'ok\nwarn\nfail'
needle=
if printf '%s\n' "$data" | grep -q "$needle"; then
    label="found"
else
    label="missing"
fi
echo "$needle:$label"
exit status Status `0` means success; non-zero means the command did not succeed.
if command `if command; then` branches using the command's exit status.
grep -q `grep -q` searches quietly and reports the result through its status.