使用 gawk 命令的正则表达式

Question

In Linux, I'm running the command

pmap -x $PID | tail -n 1

This gives me a line like the following:

total kB         168194812  870692  852296

I'm trying to extract the 2nd number (rss) for use. I found this example that works in regex101.com:

/[^\d]*[\d]+[\s]+([\d]+)/

However, when I try to run it against my line of text I don't get any print output:

echo "total kB         168194812  870692  852296" | gawk 'match($0, /[^\d]*[\d]+[\s]+([\d]+)/, a) {print a[1]}'

I'm expecting it to print

870692

Answer 1

Like this:

$ pmap -x $PID | gawk 'match($0, /[^0-9]*[0-9]+\s+([0-9]+)/, a) {print a[1]}'
870692

The expression \d is specific Perl/PCRE compatible regex. Some languages like Python use this too.

You can simplify to:

awk '{print $4}'

Using grep :

grep -oP '\d+(?=\s+\d+$)'

Answer 2

What about just displaying the 4th field with

awk '{print $4}'

With your example

echo "total kB         168194812  870692  852296" | awk '{print $4}'

returns

870692

Answer 3

With GNU grep and with your shown samples please try following grep code. Here is the complete Online regex demo for used regex.

echo "total kB         168194812  870692  852296" |
grep -oP '^total kB\s+\d+\s+\K\d+'

Explanation:

• I am using -oP options of GNU grep here, which are for exact matching and enabling PCRE regex flavour respectively.
• Then in main grep program I am using regex ^total kB\s+\d+\s+\K\d+ where:
• Matching total kB from starting of the value followed by spaces followed by digits followed by spaces.
• Then using \K option to forget values whatever matched till now by regex, this will help us to get the required output, though it matches the regex but doesn't consider values in output printing.
• Then matching 1 or more digits which is our required output.

Answer 4

If you want to use awk you can match digits with [0-9] and the negated version [^0-9]

As you output a single line with tail -n 1 , using gnu awk you could also set the row separator to 1 or more digits, and print the row terminator when the row number is 2.

echo "total kB         168194812  870692  852296" | 
awk -v RS='[0-9]+' 'NR == 2 {print RT}'

Output

870692