Toolbox Aid

August 12th, 2024 12:15 PM Mr. Q Categories: Command

awk: Pattern Scanning and Processing Language

Description: awk is a powerful text-processing language used for pattern scanning and reporting. It is particularly useful for handling data in text files and performing complex text manipulations and report generation.

Common Arguments:

• -f file: Specifies a file containing awk commands.
• -F fs: Sets the field separator to fs.
• -v var=value: Passes a variable to the awk program.
• -e script: Specifies the awk script directly.

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Sample Code and Usage:

Command:

awk -F ',' '{ print $1, $2 }' file.csv

Sample File (file.csv):

Name,Age,Occupation
Alice,30,Engineer
Bob,25,Designer
Charlie,35,Manager

Execution:

$ awk -F ',' '{ print $1, $2 }' file.csv
Name Age
Alice 30
Bob 25
Charlie 35

Explanation:

• -F ',': Sets the field separator to a comma, so awk treats each line as a set of fields separated by commas.
• { print $1, $2 }: The awk script prints the first and second fields of each line.

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Pre File View:

Command:

cat file.csv

Sample Output:

Name,Age,Occupation
Alice,30,Engineer
Bob,25,Designer
Charlie,35,Manager

Post File View:

Execution:

$ awk -F ',' '{ print $1, $2 }' file.csv
Name Age
Alice 30
Bob 25
Charlie 35

Explanation of File Views:

• Pre File View: Shows the original content of the file with comma-separated values.
• Post File View: Shows the output of the awk command, displaying only the first two columns from the CSV file.

And yes, awk can work with various file types as long as the files contain text. It is not limited to CSV files but can handle any text-based files. Here are some examples:

Text Files

Command:

awk '{ print $1 }' textfile.txt

Sample File (textfile.txt):

Hello World
This is a test
Awk is powerful

Sample Output:

Hello
This
Awk

Explanation:

• The command prints the first word ($1) from each line of a plain text file.

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Log Files

Command:

awk '/ERROR/ { print $0 }' logfile.log

Sample File (logfile.log):

INFO 2024-08-01 Everything is OK
ERROR 2024-08-02 Something went wrong
INFO 2024-08-03 All systems nominal
ERROR 2024-08-04 Another error occurred

Sample Output:

ERROR 2024-08-02 Something went wrong
ERROR 2024-08-04 Another error occurred

Explanation:

• The command searches for lines containing the string ERROR and prints them.

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TSV (Tab-Separated Values) Files

Command:

awk -F '\t' '{ print $1, $3 }' file.tsv

Sample File (file.tsv):

Name\tAge\tOccupation
Alice\t30\tEngineer
Bob\t25\tDesigner
Charlie\t35\tManager

Sample Output:

Name Occupation
Alice Engineer
Bob Designer
Charlie Manager

Explanation:

• -F '\t': Sets the field separator to a tab character, allowing awk to process TSV files.

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JSON Files

Command:

cat file.json | awk '/"name":/ { print $2 }'

Sample File (file.json):

{
    "name": "Alice",
    "age": 30,
    "occupation": "Engineer"
}

Sample Output:

"Alice",

Explanation:

• This command extracts values associated with the name key from a JSON file. Note that for more complex JSON parsing, tools like jq are recommended.

Summary

awk is a versatile tool capable of processing various text-based file types. It is effective for tasks involving pattern matching, field extraction, and text manipulation across different formats.