Truncate log files such that the end of the file is preserved

logtrunc

#! /bin/bash

# Truncate to last 100 lines of each file.
# logtrunc file1 file2 file3

# Truncate to last 50 lines of each file.
# logtrunc -n 50 file1 file2 file3

# WARNING * WARNING * WARNING
# This script is not highly tested
# WARNING * WARNING * WARNING

# Set a default for the number of lines printed
NUMLINES=100

while `true`; do

    # Enable interactive mode
    if [[ $1 =~ ^(-i|--interactive)$ ]]; then
        INTERACTIVE=1;

    # Allow -n 100 for example
    elif [[ $1 =~ ^-n$ ]]; then
        NUMLINES=$2;
        shift;

    # Allow -100 for example
    elif [[ $1 =~ ^-[0-9]+$ ]]; then
        NUMLINES=${1##-};

    # Read -h or --help and then exit
    elif [[ $1 =~ ^(-h|--help)$ ]]; then
        echo "logtrunc [[ OPTIONS ]] <files>";
        echo "         -n <number>        Trim to the last n lines";
        echo "         -<number>";
        echo "                  "; 
        echo "         -d, --dry-run      Only print don't truncate";
        echo "         -i, --interactive  Ask before trunacting";
        echo "         -h, --help         How meta";
        echo "                  ";
        echo "Version: 0.1.0"
        echo "Author: cdosborn"
        exit 0;

    elif [[ $1 =~ ^(-d|--dry-run)$ ]]; then
        DRYRUN=1;

    # We didn't parse an option
    else
        break;
    fi

    # Pop off last option
    shift;
done;

if [[ $INTERACTIVE && $DRYRUN ]]; then
    echo "** Error incomatible options: interactive, dry run";
    exit 1;
fi;

FILES=$@;

# Truncate a file to its last n lines;
# trunc n file
function trunc {
    tail -n "$1" < "$2" > "$2.bak";
    mv "$2.bak" "$2";
}

for file in $FILES; do

    # Silently skip directories
    if [[ -d "$file" ]]; then
        continue;
    fi;

    # Continue if not a regular file
    if [[ ! -f "$file" ]]; then
        echo "Cannot find file \"$file\"";
        continue;
    fi;

    LENGTH="$(wc -l < "$file" 2>&-)";

    # File needs to be truncated
    if [[ "$LENGTH" -gt "$NUMLINES" ]]; then
        if [[ $DRYRUN ]]; then 
            echo "(dry run) Trimming $file";
            continue;
        fi;

        if [[ ! $INTERACTIVE ]]; then 
            echo "Trimming $file";
            trunc $NUMLINES $file
            continue;
        fi;

        # Prompt to truncate file
        read -ep "Trim $file? (y/N/q) " answer;

        if [[ "$answer" =~ ^(q|Q)$ ]]; then
            echo "Quitting.";
            exit 0;
        elif [[ "$answer" =~ ^(y|Y)$ ]]; then
            echo "Trimmming $file"
            trunc $NUMLINES $file
        else
            echo "Skipping $file"
        fi
    else
        echo "Skipping $file of length $LENGTH"
    fi
done;

+1