awk Programming

Built-in Variables

Like many programming languages, awk has special variables that are available all the time. Following is a list of some common and useful ones.

Since awk deals with records and fields, there are built-in variables for them. Here are some of them:

FS (Field Separator)
The character or regex that is used to separate fields. Default is a space.
RS (Record Separator)
The character that separates records. By default the newline character, but can be reset using this variable.
NF (Number of Fields)
Number of fields in current record.
Example:
```
awk 'BEGIN {FS=":"}; {print NF }' names.txt
```
OFS (Output Field Separator)
Single space is the default. Any string of characters can be used. Usually used with a print statement.
ORS (Output Record Separator)
Default is a newline character '\n' and is output at the end of every print statement. Can be changed.
FNR (File Number of Records)
Number of records (lines) that have been read from current input file.
Example:
```
awk 'END {print FNR}' names.txt
```
NR (Number of Records)
Total number of records (lines) read so far from all input files.
Example:
```
awk 'END {print NR}' names.txt
```

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