I have a variable that is created in bash, and want to use it within awk statement to create a file by concatenating it with a string for the filename.
awk -v value="${index}" 'BEGIN{}{print $9 >> "example_value.txt";}END{}'
How can I do this?
You have to use it outside of the double quotes. awk concatenates it without any other character:
awk -v value="${index}" 'BEGIN{}{print $9 >> "example_" value ".txt";}END{}'
You could use -voption as in the examples previously posted.
Or you could just use something like :
awk 'BEGIN{}{print $9 >> "example_'"$index"'.txt";}END{}'
Moreover, you don't have to use {} around the variable index in this case.
Related
I noticed when running a command that this statement doesn't recognize the delimiter
awk -F',' "{print $4}" wtd.csv
However, this one does.
awk -F',' '{print $4}' wtd.csv
Any reason why? I'm sure this is part of some general bash rule I'm forgetting.
If you're using double quotes, $4 will get replaced by Bash (probably with the empty string). You'd need to escape the $ to use it in double quotes.
Example where this also is happening:
[thom#lethe ~]$ echo '$4'
$4
[thom#lethe ~]$ echo "$4"
[thom#lethe ~]$ echo "\$4"
$4
You are forgetting that double-quotes allow bash variable interpolation. In this case it tries to replace $4 with the fourth argument to the shell which is usually empty.
The single-quotes prevent bash interpolation and passes the literal $4 to awk.
You'll have identical results with:
awk -F',' '{print $4}' wtd.csv
awk -F',' "{print \$4}" wtd.csv
I am having a little trouble with using a variable and printing the 2nd field with the awk command. I am attempting to grab a number from a value in a file. The value in the file looks like
MAX=10000 (I want the Number only), I am passing this into a variable in a script so in the script I have variables
parm_file=ParmFiles/Parmfile.parm
session=s_session_value
OLD_MAX_SEQ_NR=`awk -F '=' "/$session/ {getline; print $2}" < $parm_file`
because I have double quotes to identify the $session variable, it is taking the $2 as a variable too, and so it is just printing the whole line, instead of the second field.
I've tried also to pass the variable into the awk command like
OLD_MAX_SEQ_NR=`awk -F '=' \
-v var="$session" \
'/var/ {getline; print $2}' < $parm_file`
But it does not seem to be putting the variable where var is. I have even tried hard coding the -v var="s_session_value" and it does not work.
I can't figure out a way to make the command look at the $2 as it normally does instead of a variable. Any help would be greatly appreciated.
Try this:
parm_file=ParmFiles/Parmfile.parm
session=s_session_value
OLD_MAX_SEQ_NR=$(
awk -F'=' -v pat="$session" \
'$0 ~ pat {getline; print $2}' < "$parm_file"
)
You need to pass shell variables to awk by defining an awk variable using -v.
Using variable inside /../ is taken as literal. So use $0~var_name construct.
Using back-ticks is deprecated. Use command substitution $(..)
Quote your variables.
It's a bit tricky without a sample line of the parm file. But I don't understand why you don't use cut, it makes it much easier?
OLD_MAX_SEQ_NR=$(grep "$session" "$parm_file" | cut -d= -f2)
I am new to awk.I just try to write some thing that to exchange my text file.but I failed.
I want to output like 'hello'.
I used command awk '{print "'hello'"}' filename to do it.but failed:
output like: hello
but I used command awk '{print "\'hello\'"}' filename to do it.failed again:
output like: >
ok.it seems that the awk command do not get what I mean.
So I am confused about that .how to solve the problem.
guys thanks.
Using the ascii code:
awk '{print "\x27" "hello" "\x27"}' filename
Using a variable:
awk -v q="'" '{print q "hello" q}' filename
Example:
$ seq 2 > filename
$ awk '{print "\x27" "hello" "\x27"}' filename
'hello'
'hello'
$ awk -v q="'" '{print q "hello" q}' filename
'hello'
'hello'
Simply use double quotes:
awk "{print \"'hello'\"}" filename
Although that won't really modify your file.
awk '{print "'"'"'hello'"'"'"}' filename
clyfish's answer works, if you must have it output single quotes and you must use scripts that you pass on the command line.
What I usually do in cases like these, though, when I need to do quoting but I don't want to write a 'real' awk script, is this:
awk 'function q(word) { return "\"" word "\"" }
{ printf("mv %s SomeDir/;", q($0)) }'
What I've done is to define a function that returns whatever you pass it in double quotes. Then use printf to actually use it. Without doing that, I would have had to do:
awk '{ print("mv \"" $0 "\" SomeDir/;") }';
It gets pretty nasty. For more complicated examples, this can be a life saver.
However, suppose you really do need to output something with actual single quotes. In that case dealing with odd shell quoting rules while trying to pass scripts like this on the command line is going to drive you completely insane, so I would suggest you just write a simple throwaway file.
#!/usr/bin/awk
# hi.awk
{ print("'hello'") }
then call it:
awk -f ./hi.awk
You don't really even need the #! line in the file if you do it that way, but neither does it hurt.
How to use awk variable in search?
Name="jony"
awk -v name="$Name" '/name/ {print $0}' file
this will search for string name, not for $Name which is actually jony.
Correct, awk won't recogize variables in / /. You can do:
Name="jony"
awk -v name="$Name" '$0 ~ name' file
Since print is awk's default behavior we can avoid using it here.
Hope I understood problem correctly:
Why wont you try following one:
awk '/'"$Name"'/ { print } ' testfile
When writing an AWK one-liner, you could quote the script with either the single quotes or double quotes. In the latter case the shell does all the substitution directly so that you do not need to pass the variable into the script via -v option:
Name="jony"
awk "/$Name/" file
# this works. after shell has performed substitutions, the line looks like
awk "/jony/" file
[bad!] Or even without quotes if the name does not contain spaces:
awk /$Name/ file
All the simplicity vanishes as soon as you want to use $ in the script, including awk special variables that use $0, $1, etc, because you will have to escape the dollar sign to prevent shell variable expansion.
awk "/$Name/ {print \$0}"
In addition you will have to escape the double quotes to add literal text to the script. Looks clumsy:
awk "/$Name/ {print \"Found in: \" \$0}"
To crown it all, negating regular expression with double quotes will cause a shell error:
awk "!/$Name/"
#error> ... event not found ...
The error will happen if $Name itself contains ! sign. This makes using double quotes unreliable.
So, to be on the safe side, prefer single quotes :)
I have a shell script that constructs an awk program as a string then pass that string to awk. This is because I want to use values of shell variables in the awk program.
My code looks like this:
awk_prog="'{if (\$4~/$shell_var/) print \$1,\$2}'"
echo $awk_prog
awk $awk_prog $FILENAME
However, when I pass the string to awk, I always get the error:
'{if ($4~/regex/) print $1,$2}'
awk: '{if
awk: ^ invalid char ''' in expression
What does that error message mean? I tried the -F: switch but it does not help. How can I settle this issue?
Thank you.
This is caused by shell quoting. The following will work:
awk_prog="{ if (\$4 ~ /$shell_var/) print \$1, \$2 }"
echo "$awk_prog"
awk "$awk_prog" $FILENAME
When you run awk '{ print }' foo from the command line, the shell interprets and removes the quotes around the program so awk receives two arguments - the first is the program text and the second is the filename foo. Your example was sending awk the program text '{if ...}' which is invalid syntax as far as awk is concerned. The outer quotes should not be present.
In the snippet that I gave above, the shell uses the quotes in the awk_prog= line to group the contents of the string into a single value and then assigns it to the variable awk_prog. When it executes the awk "$awk_prog"... line, you have to quote the expansion of $awk_prog so awk receives the program text as a single argument.
There's another way to get your shell variable into awk -- use awk's -v option:
awk -v pattern="$shell_var" '$4 ~ pattern {print $1, $2}' "$FILENAME"
Use -v multiple times if you have several variables to pass to awk.
If you truly want to hold your awk program in a shell variable, build it up using printf:
awk_script="$( printf '$4 ~ /%s/ {print $1, $2}' "$shell_var" )"
awk "$awk_script" "$FILENAME"
Note the use of quotes in the printf command: single quotes around the template to protect the dollar signs you want awk to interpret, double quotes for shell variables.
Another (IMO simpler) solution which (I think) addresses what you are intuitively trying to do is simply to use eval. You want the shell to behave as if you had literally typed:
awk '{if ($4~/foo/) print $1,$2}' path
(where foo and path are the literal contents of $shell_var and $FILENAME). To make that happen, just slap an eval on the front of your last line (and perhaps quotes for good measure, but they aren't necessary in this case) so that your last line is:
eval "awk $awk_prog $FILENAME"