In AWK, you can extract data from text files using regular expressions and field manipulation. Here are some commonly used techniques for extracting data from text files in AWK:
– **Regular expressions:** Regular expressions are a powerful tool for searching and matching text patterns. AWK supports regular expressions in the form of patterns enclosed in forward slashes (`/`). Here are some commonly used regular expression functions:
– `match`: Searches for a pattern in a string and returns the position of the match and/or the matched substring.
– `substr`: Returns a substring of a string.
– `split`: Splits a string into an array of substrings based on a delimiter.
Here is an example of using regular expressions in AWK to extract data from a text file:
“
# Extract all email addresses from a file
{
while (match($0, /[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/)) {
print substr($0, RSTART, RLENGTH)
$0 = substr($0, RSTART + RLENGTH)
}
}
In this example, we use the `while` loop to repeat the search and extraction process until no more matches are found. We use the `match` function to search for the regular expression pattern `/[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/` in each line of the input file. This pattern matches email addresses that conform to the standard format. If a match is found, we use the `substr` function to extract the matched substring from the line, starting at the position `RSTART` and with a length of `RLENGTH`. We then use the `print` statement to print the extracted email address. Finally, we use the `substr` function to remove the matched substring from the line and repeat the search and extraction process until no more matches are found.
– **Field manipulation:** You can manipulate fields (columns) in a line using the built-in variables `$1`, `$2`, etc., and the `NF` variable. Here are some commonly used field-related functions:
– `split`: Splits a string into an array of substrings based on a delimiter.
– `substr`: Returns a substring of a string.
Here is an example of using field manipulation in AWK to extract data from a text file:
`
# Extract the first and last names from a CSV file
BEGIN {
FS = “,”
}
{
split($2, names, ” “)
first = names[1]
last = names[length(names)]
print first, last
}
`
In this example, we use the `split` function to split the second field of each lineinto an array of substrings based on a space delimiter. We then use the `names` array to store the substrings that correspond to the first and last names. We use the `first` and `last` variables to store the first and last names, respectively, and then use the `print` statement to print them.
These are just a few examples of the techniques that you can use in AWK to extract data from text files. You can combine these techniques with other AWK features to implement complex data processing and analysis tasks.