Which exit status should a deployment‑check script treat as success when grep finds no matches?

Answer

When the goal is to verify that a log contains no error lines, a grep exit status of 1 (no matches) should be treated as a successful "no errors found" result.

Confirmed facts

• grep returns 0 when at least one line matches the pattern.
• grep returns 1 when the pattern is found in zero lines (no matches).
• grep returns 2 only when it cannot open or read the input file (missing file, permission problems, etc.).
• If head terminates the pipeline early, grep receives SIGPIPE and exits with status 141; the pipeline’s overall status becomes 141, but this does not indicate a log problem.

Recommended steps for a script using set -e and set -o pipefail

1. Run the grep … | head pipeline as usual.
2. Immediately after the pipeline, inspect the PIPESTATUS array to obtain each command’s exit code:

#!/usr/bin/env bash
set -euo pipefail

# Example: look for lines containing ERROR in a log file
grep -E 'ERROR' "$logfile" | head -n 20
# Capture exit codes
local grep_status=${PIPESTATUS[0]}
local head_status=${PIPESTATUS[1]}

case "$grep_status" in
    0)  echo "Error lines found – investigation needed." ;;
    1)  echo "No error lines found – success." ;;   # treat as success
    2)  echo "Unable to read log file – failure." >&2; exit 2 ;;
    141) echo "head truncated grep output – treat as success (no matches needed)." ;;
    *)  echo "Unexpected grep exit status $grep_status" >&2; exit "$grep_status" ;;
esac

1. Based on the grep_status value, decide:
   • 0 → matches found → treat as failure (error present).
   • 1 → no matches → treat as success (no errors).
   • 2 → file error → treat as failure.
   • 141 → SIGPIPE from head → treat as success (or ignore) because it only means head stopped after getting enough output.

Missing diagnostic detail

If you need to be certain that all matching lines are examined (i.e., you cannot tolerate head truncating the output), please confirm whether treating the SIGPIPE case as success is acceptable, or if you prefer to disable head or use a different limiter (e.g., grep -m N). This detail changes whether you should treat exit 141 as success or as a condition requiring further handling.