bash script input file stream - ghdrako/doc_snipets GitHub Wiki

Reading Input from Files:

Bash scripts can read data from files using commands like cat, read, or <.

• Example using cat:

filename: read_file_example.sh
filename="example.txt"
while IFS= read -r line; do
echo "Line read from file: $line"
done < "$filename"

• Example using read:

filename: read_file_example.sh
filename="example.txt"
while read -r line; do
echo "Line read from file: $line"
done < "$filename"

Handling Input Streams

Input streams refer to data provided to a script through mechanisms like command substitution ($(command)), pipelines (|), or process substitution (<(command)).

• Example using Command Substitution:

filename: command_substitution.sh
result=$(ls -l)
echo "List of files: $result"

• Example using Pipelines:

filename: pipeline_example.sh
cat example.txt | grep "keyword"

Reading Input Line by Line

To process input line by line, read command is often used in combination with loops.

• Example:

filename: line_by_line.sh
while IFS= read -r line; do
echo "Processing line: $line"
done

Reading Specific Columns from Input

For structured data, awk or cut commands are useful for extracting specific columns.

• Example using awk:

filename: extract_column.sh
cat data.csv | awk -F',' '{print $2}'

• Example using cut:

filename: extract_column.sh
cut -d',' -f2 data.csv

Processing Input with sed and grep

sed and grep are powerful tools for manipulating and filtering text in input streams.

• Example using sed:

filename: sed_example.sh
cat data.txt | sed 's/old/new/g'

• Example using grep:

filename: grep_example.sh
cat log.txt | grep "error"

Redirecting Output to Files

Output from scripts can be redirected to files using > or >>`` operators.

• Example:

filename: output_to_file.sh
echo "Hello, World!" > output.txt

Processing Multiple Files

Bash scripts can process multiple files using wildcards or loops.

• Example using Wildcards:

filename: process_files.sh
for file in .txt; do
echo "Processing file: $file"
done

Interacting with User Input

Scripts can prompt users for input using the read command.

• Example:

filename: user_input.sh
echo "Enter your name:"
read username
echo "Hello, $username!"

Handling Binary Input

Binary input, such as images or executables, can be read using commands like hexdump or od.

• Example:

filename: hexdump_example.sh
hexdump -C binary_file.bin