Awk

• awk ’{print}’ test.sh
• awk ’{print $0}’ test.sh
• cat /etc/shells | awk …
• awk … /etc/shells =FIELD SEPARATORS
• awk ’BEGIN{FS=“:”; OFS=“-”} {print $1,$6,$7}’ /etc/passwd
• cat etc/shells | awk ’^\ {print $0}’
• cat etc/shells | awk ’^\ {print $NF}’ awk -F “/” ’/^\//{print $NF}’ /etc/shells | uniq
• awk -F “:” ’ {print $2}’ /etc/passwd

ps -ef | awk '/root/ && $2<100'
ps -ef | awk '/root/ || /dt/ && (length($NF) < 30)'

• ps -ef | head | awk ’{print $1“ ”$8}’
• show \t \n as alternative to just “ ”
• show $NF instead of $8

/\[/

• df | awk ’\/dev\/loop {print $1“\t”$2“\t”$3}’
• df | awk ’\/dev\/loop {print $1“\t”$2 - $3}’

awk 'length($0) > 7' /etc/shells

ps -ef | awk '{ if($NF == "/bin/fish") print $0};'

The ~ is the regular expression match operator. It checks if a string matches the provided regular expression.

awk '$1 ~ /^[b,c]/ {print $0}' .bashrc

We use the substr() function. It prints a substring from the given string. We apply the function on each line, skipping the first three characters. In other words, we print each record from the fourth character till its end.

awk '{print substr($0, 4)}'  numbered.txt

The match() function sets the RSTART variable; it is the index of the start of the matching pattern.

awk 'match($0, /o/) {print $0 " has \"o\" character at " RSTART}' numbered.txt

NR command keeps a current count of the number of input records. Remember that records are usually lines. Awk command performs the pattern/action statements once for each record in a file.

NF command keeps a count of the number of fields within the current input record. We’ve already shown using $NF for last field.

Using NF to print all non-empty lines

awk 'NF > 0' /etc/shells

FS command contains the field separator character which is used to divide fields on the input line. The default is “white space”, meaning space and tab characters. FS can be reassigned to another character (typically in BEGIN) to change the field separator.

RS command stores the current record separator character. Since, by default, an input line is the input record, the default record separator character is a newline.

OFS command stores the output field separator, which separates the fields when Awk prints them. The default is a blank space. Whenever print has several parameters separated with commas, it will print the value of OFS in between each parameter.

ORS command stores the output record separator, which separates the output lines when Awk prints them. The default is a newline character. print automatically outputs the contents of ORS at the end of whatever it is given to print.