| name | combined-head-linecount-check |
| description | Verify a file's first N lines and total line count in one shell call using head and wc -l with an echo separator, minimizing read operations and shell iterations. |
Combined Head + Line Count Check
When you need to both inspect the top of a file and confirm its total line count, collapse the two checks into a single run_shell call instead of issuing two separate commands.
Why
- Each shell call is a round-trip. Two separate calls (
head then wc -l) cost two iterations.
- A combined call costs one iteration and returns both pieces of information atomically.
- When checking multiple files at once, each file still only needs one call (or all files can be parallelized in a single compound command).
Pattern
head -N <file> && echo "---" && wc -l <file>
The echo "---" separator makes the output easy to parse visually: everything above the dashes is content, everything below is the line count.
Examples
Single file — inspect first 10 lines and total count
head -10 src/main.ts && echo "---" && wc -l src/main.ts
Sample output:
import { createApp } from 'vue'
import App from './App.vue'
...
---
142 src/main.ts
Multiple files — fully parallelized
When you need to check several files simultaneously, run them all in one shell call using && chains or newline-separated subshells:
(head -10 src/main.ts && echo "---" && wc -l src/main.ts) && echo "===" && \
(head -10 vite.config.ts && echo "---" && wc -l vite.config.ts) && echo "===" && \
(head -5 package.json && echo "---" && wc -l package.json)
Or, if order independence is acceptable, run them in parallel background jobs and wait:
{
head -10 src/main.ts && echo "---" && wc -l src/main.ts
} &
{
head -10 vite.config.ts && echo "---" && wc -l vite.config.ts
} &
wait
When to Apply
| Situation | Recommendation |
|---|
| Verifying a generated/modified file was written correctly | ✅ Use combined call |
| Checking multiple output files after a build step | ✅ Parallelize all in one shell call |
| Only need line count (no content preview required) | Use plain wc -l |
| Only need content (no line count required) | Use plain head -N |
| File is extremely large and you want a middle section | Use sed -n or awk instead |
Integration with Parallel Reads
This pattern compounds well with parallel file reads. In a single iteration you can:
- Read file contents with
cat or head for multiple files.
- Simultaneously verify line counts with
wc -l.
- Check for specific patterns with
grep -c.
Example of a 5-file parallel verification in one shell call:
echo "=== main.ts ===" && head -10 src/main.ts && echo "lines:" && wc -l < src/main.ts && \
echo "=== config ===" && head -5 vite.config.ts && echo "lines:" && wc -l < vite.config.ts && \
echo "=== package ===" && head -5 package.json && echo "lines:" && wc -l < package.json && \
echo "=== index ===" && head -8 index.html && echo "lines:" && wc -l < index.html && \
echo "=== readme ===" && head -5 README.md && echo "lines:" && wc -l < README.md
Tip: Using wc -l < file (with input redirect) prints only the number, without the filename — cleaner output when the filename is already shown by the echo label above it.
Key Takeaway
Never use two shell calls where one will do. Combining head -N and wc -l in a single command is the minimal-overhead way to answer both "what does this file contain?" and "is it the right size?" simultaneously.
