Automating system tasks with awk

In AWK, you can automate system tasks by using a combination of built-in variables, functions, and control structures to interact with system resources and perform repetitive tasks. Here are some commonly used techniques for automating system tasks with AWK:

– **Built-in variables:** AWK provides several built-in variables that you can use to automate system tasks. Here are some commonly used built-in variables:

– `ENVIRON`: An array of environment variables.
– `FILENAME`: The name of the current input file.
– `FS`: The input field separator.
– `RS`: The input record separator.

Here is an example of using built-in variables in AWK to automate system tasks:

“
# Search for a pattern in all files in a directory
BEGIN {
pattern = “error”
FS = “:”
print “Searching for pattern \”” pattern “\” in all files in the current directory…”
}
{
if ($2

 pattern) {
      print "File: " FILENAME ", Line: " NR ", Match: " $0
    }
  }
  

  
  In this example, we use the `ENVIRON` array to access environment variables. We use the `FILENAME` variable to get the name of the current input file, and the `FS` variable to set the input field separator. We use the `RS` variable to set the input record separator.

- **Functions:** AWKprovides several functions that you can use to automate system tasks. Here are some commonly used functions:

  - `system`: Executes a shell command.
  - `strftime`: Formats a date and time string.
  - `getline`: Reads the next input line into a variable.

  Here is an example of using functions in AWK to automate system tasks:

  

`
  # Rotate log files daily
  BEGIN {
    log_dir = "/var/log"
    log_file = "app.log"
    date_format = "%Y-%m-%d"
    today = strftime(date_format)
    old_log = log_dir "/" log_file "." today
    new_log = log_dir "/" log_file
    cmd = "mv " new_log " " old_log
    system(cmd)
    print "Rotated log file: " old_log " -> " new_log
  }
  

`

  In this example, we use the `strftime` function to format a date string in the format "YYYY-MM-DD". We use this date string to construct the names of the old and new log files. We use the `system` function to execute a shell command that renames the current log file to the old log file. We use the `print` statement to output a message indicating that the log file was rotated.

- **Control structures:** You can use control structures (`if`, `else`, `while`, etc.) to implement automation logic in your AWK scripts. Here is an example of using a `while` loop in AWK to automate system tasks:

  

`
  # Monitor a log file for new errors
  BEGIN {
    log_file = "/var/log/app.log"
    pattern = "error"
    print "Monitoring " log_file " for new errors..."
  }
  {
    while (getline < log_file > 0) {
      if ($0 

pattern && !seen[$0]) {
print “New error: ” $0
seen[$0] = 1
}
}
close(log_file)
sleep(60)
}

`

In this example, we use a `while` loop to read new lines from the log file (`log_file`). We use the `getline` function to read the next line of input from the file, and the `close` function to close the file when we are done. We use the `sleep` function to pause the script for 60 seconds before checking for new errors again.

These are just a few examples of the techniques that you can use in AWK to automate system tasks. Remember that AWK is a powerful tool for text processing and manipulation, and can be used to automate a wide range of system administration tasks.