Links & files

Awk reference and ressources	Example files
gnu.org	`mail-list`
oreilly effective awk programming	`inventory-shipped`

📑 Printing Output#

print Statement#

print item1, item2, …

awk 'BEGIN { print "Month Crates"
     print "----- ------" }
   { printf "%-5s %s\n", $1, $2 }' inventory-shipped

Output separators#

OFS The output field separator, a space by default.

ORS The output record separator, by default a newline.

awk 'BEGIN { OFS = ";"; ORS = "\n\n" } { print $1, $2 }' mail-list

Numeric output with print#

OFMT The output format for numbers, “%.6g”, by default.

awk 'BEGIN {
OFMT = "%.0f"
print 17.23, 17.54 }'

printf Statements#

printf format, item1, item2, …

awk 'BEGIN {
ORS = "\nOUCH!\n"; OFS = "+"
msg = "Don\47t Panic!\nBe cool!"
printf "%s\n", msg
print
print msg
}'

Format-control letters#

%c	Print a number as a character
%d , %i	Print a decimal integer
%e , %E	Print a number in scientific (exponential) notation
%f	Print a number in floating-point notation
%s	Print a string

awk 'BEGIN { printf "%s%c%s\n", "Don", 39, "t Panic" }'

awk 'BEGIN { printf "%s\n", "string"
printf "%4.3e\n", 1950
printf "%4.3f\n", 1950
printf "%c\n", 65
}'

awk 'BEGIN { FS = ":" } $3 > 999 {
printf "Name: %s\nUID: %d\nShell: %s\n", $1, $3, $7
}' /etc/passwd

Modifiers for printf Formats#

N$ positional specifier

awk 'BEGIN { printf "%3$s%2$c%1$s\n", "t Panic", 39, "Don"}'

(-)width width modifier

awk 'BEGIN { printf "%4s", "foo" }'
awk 'BEGIN { printf "%6s", "foo" }'
awk 'BEGIN { printf "%-6s", "foo" }'
awk 'BEGIN { printf "%-4s", "foo" }'

.number maximum number of characters from the string

awk 'BEGIN { s = "ABCDEFG" ; printf "%5.3s\n", s }'
   ABC

Examples using printf#

awk '(NR <= 1) || (NR >= 11) { printf "%10s %s\n", $1, $2 }' mail-list

   Amelia 555-5553
Jean-Paul 555-2127

awk '(NR <= 1) || (NR >= 11) { printf "%-10s %s\n", $1, $2 }' mail-list

Amelia     555-5553
Jean-Paul  555-2127

awk 'BEGIN { format = "%-10s %s\n"
printf format, "Name", "Number"
printf format, "----", "------"
}
(NR <= 1) || (NR >= 11) {
printf format, $1, $2
}' mail-list

Name       Number
----       ------
Amelia     555-5553
Jean-Paul  555-2127

awk 'BEGIN { "cat mail-list | wc -l" | getline num_line
close("cat mail-list | wc -l")
format = "%-10s %s\n"
printf format, "Name", "Number"
printf format, "----", "------" }
(NR <= 1) || (NR >= num_line) {
printf format, $1, $2 }' mail-list

Redirecting output#

print items > output-file

awk '{ print $2 > "phone-list"
print $1 > "name-list"
}' mail-list

print items >> output-file

awk 'BEGIN { "cat mail-list | wc -l" | getline num_line
close("cat mail-list | wc -l")}
(NR <= 1) || (NR >= num_line) {
print $2 >> "phone-list" }' mail-list

print items | command

awk '{ command = "sort -r"
print $1 | command }' mail-list

print items |& command

command is a coprocess.

Piping into sh#

ls -1 | awk '$0 ~ /[A-Z]+/ \
{ printf "mv %s %s\n", $0, tolower($0) | "sh" }
END { close("sh") }'

Special files for standard preopened data streams#

`/dev/tty`	represents the “terminal”
`/dev/stdin`	standard input
`/dev/stdout`	standard output
`/dev/stderr`	standard error
`/dev/fd/N`	file descriptor N

Network communications#

/net-type/protocol/local-port/remote-host/remote-port

Used with the ‘ |& ’ operator for communicating with a coprocess.

Closing input and output redirections#

close(filename)
close(command)
Its value must exactly match the string that was used to open the file
or start the command.
For coprocesses, it is possible to close only one direction of the
communications.

awk '{ command = "sort -r"
print $1 | command }
END { close(command) }' mail-list

📑 Printing Output

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