Shell Scripting

Frequently Used Command Line Tools

tr

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sort

…

uniq

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awk

…

basename

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Real World Problems

Word Frequency Count

# Read from the file words.txt and output the word frequency list to stdout.
tr -s '[:space:]' '\n' < words.txt | sort | uniq -c | sort -nr | awk '{print $2, $1}'

Add Prefix to All the Files in a Directory

Run the following command:

chmod +x add_prefix.sh
./add_prefix.sh /path/to/directory prefix_

And here is the add_prefix.sh:

#!/bin/bash

# Check if the directory and prefix are provided as arguments
if [ $# -ne 2 ]; then
    echo "Usage: $0 <directory> <prefix>"
    exit 1
fi

# Assign arguments to variables
directory=$1
prefix=$2

# Check if the directory exists
if [ ! -d "$directory" ]; then
    echo "Error: Directory $directory does not exist."
    exit 1
fi

# Iterate over all files in the directory
for file in "$directory"/*; do
    # Skip directories
    if [ -f "$file" ]; then
        # Extract the base name of the file
        basename=$(basename "$file")
        # Rename the file with the prefix
        mv "$file" "$directory/$prefix$basename"
    fi
done

echo "Prefix added to all files in $directory."

Change Prefix from One to Another

#!/bin/bash

# Check if the directory, old prefix, and new prefix are provided as arguments
if [ $# -ne 3 ]; then
    echo "Usage: $0 <directory> <old_prefix> <new_prefix>"
    exit 1
fi

# Assign arguments to variables
directory=$1
old_prefix=$2
new_prefix=$3

# Check if the directory exists
if [ ! -d "$directory" ]; then
    echo "Error: Directory $directory does not exist."
    exit 1
fi

# Iterate over all files in the directory
for file in "$directory"/*; do
    # Skip directories
    if [ -f "$file" ]; then
        # Extract the base name of the file
        basename=$(basename "$file")

        # Check if the file name starts with the old prefix
        if [[ "$basename" == "$old_prefix"* ]]; then
            # Remove the old prefix and add the new prefix
            new_name="$new_prefix${basename#$old_prefix}"
            # Rename the file
            mv "$file" "$directory/$new_name"
        fi
    fi
done

echo "Prefix changed from '$old_prefix' to '$new_prefix' in $directory."

References

• word-frequency
• Rename multiple files with prefix or suffix in Linux console
• Remove a fixed prefix/suffix from a string in Bash
• Shell Parameter Expansion