I'd like to execute the following awk script (which is working well) in tcl:
exec awk {$1=="text" {print $0}} temp1.txt > temp2.txt}
BUT the problem is that "text" is comming from TK entry widget and I have to put it in a variable ($var) which is not recognized by awk:
set var [.entry get]
exec awk {$1==$var {print $0}} temp1.txt > temp2.txt}
Any idea how to skip it or make it running?
PS I'd like to stay with awk, not to change the code on tcl if it's possible.
Regards,
lucas
Use -v switch in awk to pass external variable to awk:
exec awk -v var=$var {$1==var {print $0}} temp1.txt > temp2.txt}
Related
hello i have the following awk script:
#!/bin/awk -f
{for(i=4;i<=7;i++) j+=$i; print "Student",NR",",$1,$2",",j/4; j=0}
and i want to append the output to a new file (newfile.txt).
Could you please try following. Where mention output file inside awk code itself.
{for(i=4;i<=7;i++) j+=$i; print "Student" OFS NR",",$1,$2"," OFS j/4 >> (output_file); j=0}
OR 2nd way is when you are running your awk code where script is the script name you are calling to run your awk program eg-->
./script >> output_file
In case you want to run an awk one-liner to get output into a output file then try following.
awk -v output_file="Output.txt" '{for(i=4;i<=7;i++) j+=$i; print "Student" OFS NR",",$1,$2"," OFS j/4 >> (output_file); j=0}' Input_file
In above code I have created a variable named output_file whose value you could keep it as per your wish too.
Don't use a shebang to call awk from a shell script as it robs you of the ability to separate your functionality by what each (the shell or awk) does best. Make your shell script look like this instead (using whichever shell you use for the shebang):
#!/bin/env bash
awk '
{for(i=4;i<=7;i++) j+=$i; print "Student",NR",",$1,$2",",j/4; j=0}
' "$#" >> newfile.txt
I found some ways to pass external shell variables to an awk script, but I'm confused about ' and ".
First, I tried with a shell script:
$ v=123test
$ echo $v
123test
$ echo "$v"
123test
Then tried awk:
$ awk 'BEGIN{print "'$v'"}'
$ 123test
$ awk 'BEGIN{print '"$v"'}'
$ 123
Why is the difference?
Lastly I tried this:
$ awk 'BEGIN{print " '$v' "}'
$ 123test
$ awk 'BEGIN{print ' "$v" '}'
awk: cmd. line:1: BEGIN{print
awk: cmd. line:1: ^ unexpected newline or end of string
I'm confused about this.
#Getting shell variables into awk
may be done in several ways. Some are better than others. This should cover most of them. If you have a comment, please leave below. v1.5
Using -v (The best way, most portable)
Use the -v option: (P.S. use a space after -v or it will be less portable. E.g., awk -v var= not awk -vvar=)
variable="line one\nline two"
awk -v var="$variable" 'BEGIN {print var}'
line one
line two
This should be compatible with most awk, and the variable is available in the BEGIN block as well:
If you have multiple variables:
awk -v a="$var1" -v b="$var2" 'BEGIN {print a,b}'
Warning. As Ed Morton writes, escape sequences will be interpreted so \t becomes a real tab and not \t if that is what you search for. Can be solved by using ENVIRON[] or access it via ARGV[]
PS If you have vertical bar or other regexp meta characters as separator like |?( etc, they must be double escaped. Example 3 vertical bars ||| becomes -F'\\|\\|\\|'. You can also use -F"[|][|][|]".
Example on getting data from a program/function inn to awk (here date is used)
awk -v time="$(date +"%F %H:%M" -d '-1 minute')" 'BEGIN {print time}'
Example of testing the contents of a shell variable as a regexp:
awk -v var="$variable" '$0 ~ var{print "found it"}'
Variable after code block
Here we get the variable after the awk code. This will work fine as long as you do not need the variable in the BEGIN block:
variable="line one\nline two"
echo "input data" | awk '{print var}' var="${variable}"
or
awk '{print var}' var="${variable}" file
Adding multiple variables:
awk '{print a,b,$0}' a="$var1" b="$var2" file
In this way we can also set different Field Separator FS for each file.
awk 'some code' FS=',' file1.txt FS=';' file2.ext
Variable after the code block will not work for the BEGIN block:
echo "input data" | awk 'BEGIN {print var}' var="${variable}"
Here-string
Variable can also be added to awk using a here-string from shells that support them (including Bash):
awk '{print $0}' <<< "$variable"
test
This is the same as:
printf '%s' "$variable" | awk '{print $0}'
P.S. this treats the variable as a file input.
ENVIRON input
As TrueY writes, you can use the ENVIRON to print Environment Variables.
Setting a variable before running AWK, you can print it out like this:
X=MyVar
awk 'BEGIN{print ENVIRON["X"],ENVIRON["SHELL"]}'
MyVar /bin/bash
ARGV input
As Steven Penny writes, you can use ARGV to get the data into awk:
v="my data"
awk 'BEGIN {print ARGV[1]}' "$v"
my data
To get the data into the code itself, not just the BEGIN:
v="my data"
echo "test" | awk 'BEGIN{var=ARGV[1];ARGV[1]=""} {print var, $0}' "$v"
my data test
Variable within the code: USE WITH CAUTION
You can use a variable within the awk code, but it's messy and hard to read, and as Charles Duffy points out, this version may also be a victim of code injection. If someone adds bad stuff to the variable, it will be executed as part of the awk code.
This works by extracting the variable within the code, so it becomes a part of it.
If you want to make an awk that changes dynamically with use of variables, you can do it this way, but DO NOT use it for normal variables.
variable="line one\nline two"
awk 'BEGIN {print "'"$variable"'"}'
line one
line two
Here is an example of code injection:
variable='line one\nline two" ; for (i=1;i<=1000;++i) print i"'
awk 'BEGIN {print "'"$variable"'"}'
line one
line two
1
2
3
.
.
1000
You can add lots of commands to awk this way. Even make it crash with non valid commands.
One valid use of this approach, though, is when you want to pass a symbol to awk to be applied to some input, e.g. a simple calculator:
$ calc() { awk -v x="$1" -v z="$3" 'BEGIN{ print x '"$2"' z }'; }
$ calc 2.7 '+' 3.4
6.1
$ calc 2.7 '*' 3.4
9.18
There is no way to do that using an awk variable populated with the value of a shell variable, you NEED the shell variable to expand to become part of the text of the awk script before awk interprets it. (see comment below by Ed M.)
Extra info:
Use of double quote
It's always good to double quote variable "$variable"
If not, multiple lines will be added as a long single line.
Example:
var="Line one
This is line two"
echo $var
Line one This is line two
echo "$var"
Line one
This is line two
Other errors you can get without double quote:
variable="line one\nline two"
awk -v var=$variable 'BEGIN {print var}'
awk: cmd. line:1: one\nline
awk: cmd. line:1: ^ backslash not last character on line
awk: cmd. line:1: one\nline
awk: cmd. line:1: ^ syntax error
And with single quote, it does not expand the value of the variable:
awk -v var='$variable' 'BEGIN {print var}'
$variable
More info about AWK and variables
Read this faq.
It seems that the good-old ENVIRON awk built-in hash is not mentioned at all. An example of its usage:
$ X=Solaris awk 'BEGIN{print ENVIRON["X"], ENVIRON["TERM"]}'
Solaris rxvt
You could pass in the command-line option -v with a variable name (v) and a value (=) of the environment variable ("${v}"):
% awk -vv="${v}" 'BEGIN { print v }'
123test
Or to make it clearer (with far fewer vs):
% environment_variable=123test
% awk -vawk_variable="${environment_variable}" 'BEGIN { print awk_variable }'
123test
You can utilize ARGV:
v=123test
awk 'BEGIN {print ARGV[1]}' "$v"
Note that if you are going to continue into the body, you will need to adjust
ARGC:
awk 'BEGIN {ARGC--} {print ARGV[2], $0}' file "$v"
I just changed #Jotne's answer for "for loop".
for i in `seq 11 20`; do host myserver-$i | awk -v i="$i" '{print "myserver-"i" " $4}'; done
I had to insert date at the beginning of the lines of a log file and it's done like below:
DATE=$(date +"%Y-%m-%d")
awk '{ print "'"$DATE"'", $0; }' /path_to_log_file/log_file.log
It can be redirect to another file to save
Pro Tip
It could come handy to create a function that handles this so you dont have to type everything every time. Using the selected solution we get...
awk_switch_columns() {
cat < /dev/stdin | awk -v a="$1" -v b="$2" " { t = \$a; \$a = \$b; \$b = t; print; } "
}
And use it as...
echo 'a b c d' | awk_switch_columns 2 4
Output:
a d c b
How to print the file name in the loop? I want to print the file name and the average value of column 4 at same line:
for i in `ls *cov`
do
awk '{sum +=$4;n++}END{print sum/n}' $i
done
I mean I want to
awk '{sum +=$4;n++}END{print $i\t sum/n}' $i
You can use bash variables in an awk script using the -v flag:
awk -v file=$i '{sum +=$4;n++}END{print file\t sum/n}' $i
But, there is also the built in awk variable FILENAME:
awk '{sum +=$4;n++}END{print FILENAME\t sum/n}' $i
Which is much cleaner since you aren't passing around variables.
Lose the loop (see why-is-using-a-shell-loop-to-process-text-considered-bad-practice) and just use:
awk -v OFS='\t' '{sum+=$4} ENDFILE{print FILENAME, (FNR>0 ? sum/FNR : 0); sum=0}' *cov
The above uses GNU awk for ENDFILE, there's simple tweaks for other awks but the important things are:
A surrounding shell loop is neither required nor desirable.
The variable n isn't needed since awk has builtin variables.
You have to protect yourself from divide by zero on empty files.
I want to make a function in my bash profile to shorten:
awk 'BEGIN{OFS="\t";FS="\t"}{}'
I'd like to be able to type:
awk2 '{print $0}'
And have it do:
awk 'BEGIN{OFS="\t";FS="\t"}{print $0}'
Unless it detects BEGIN in the input...in which case it would revert to the original awk functioning.
Does anyone have any idea what this function would look like?
This is easy if you use awk's -v instead of a BEGIN block.
awk2() {
awk -F'\t' -v OFS='\t' "$#"
}
The -v is used for variable assignments and does take place before line processing.
An alias would be messy, I recommend you shorten it using a bash function:
function awk2() {
awk -F "\t" -v OFS="\t" "$#"
}
I am using the below code to change an existing awk script so that I can add more and more cases with a simple command.
echo `awk '{if(/#append1/){print "pref'"$1"'=0\n" $0 "\n"} else{print $0 "\n"}}' tf.a
note that the first print is "pref'"$1"'=0\n" so it is referring to the variable $1 in its environment, not in awk itself.
The command ./tfb.a "c" should change the code from:
BEGIN{
#append1
}
...
to:
BEGIN{
prefc=0
#append1
}
...
However, it gives me everything on one line.
Does anyone know why this is?
If you take awk right out of the equation you can see what's going on:
# Use a small test file instead of an awk script
$ cat xxx
hello
there
$ echo `cat xxx`
hello there
$ echo "`cat xxx`"
hello
there
$ echo "$(cat xxx)"
hello
there
$
The backtick operator expands the output into shell "words" too soon. You could play around with the $IFS variable in the shell (yikes), or you could just use double-quotes.
If you're running a modern sh (e.g. ksh or bash, not the "classic" Bourne sh), you may also want to use the $() syntax (it's easier to find the matching start/end delimiter).
do it like this. pass the variable from shell to awk properly using -v
#!/bin/bash
toinsert="$1"
awk -v toinsert=$toinsert '
/#append1/{
$0="pref"toinsert"=0\n"$0
}
{print}
' file > temp
mv temp file
output
$ cat file
BEGIN{
#append1
}
$ ./shell.sh c
BEGIN{
prefc=0
#append1
}