Bash Script File Line Counter

Apple's "Bash Script File Line Counter" interview question challenges candidates to write a Bash script that accurately counts lines in files, often emphasizing edge cases like large files, varying line endings, or multiple inputs. It tests Bash scripting proficiency, Linux utilities (e.g., wc, awk), and infrastructure-related handling of filesystems.[1][5]

Problem Statement

Write a Bash script that takes one or more file paths as arguments and outputs the total number of lines across all files. The script must:

• Handle multiple files provided via command-line arguments.
• Correctly count lines terminated by LF (Unix), CR (old Mac), or CRLF (Windows).
• Exclude trailing empty lines or inconsistent endings if specified in variants.
• Be efficient for large files without loading everything into memory. No explicit constraints like file size limits or input count are universally stated, but typical ones include up to 100 files, each up to 1GB, on Linux/Unix systems.[5][9]

Input/Output Examples

Basic Usage: $ ./line_counter.sh file1.txt file2.txt Total lines: 42

• Input: file1.txt (5 lines), file2.txt (37 lines).
• Output: Sums to 42.[5]

Single File Example: $ ./line_counter.sh sample.txt Total lines: 10

• sample.txt content: ` Line 1 Line 2

Line 4 ... ` Counts 10 lines, including any blank ones.[3][5]

Edge Case (Empty File): $ ./line_counter.sh empty.txt Total lines: 0 Multiple Files with Errors: $ ./line_counter.sh *.log nonexistent.txt Error: nonexistent.txt: No such file Total lines: 150 Script should skip missing files gracefully.[4]

Sample Solution Approaches

Common efficient solution using wc: #!/bin/bash total=0 for file in "$@"; do if [[ -f "$file" ]]; then total=$((total + $(wc -l < "$file"))) else echo "Error: $file: No such file" >&2 fi done echo "Total lines: $total" This avoids forking wc per byte count for better performance on large inputs.[9][5]