I am using a script like below
SCRIPT
declare -a GET
i=1
awk -F "=" '$1 {d[$1]++;} {for (c in d) {GET[i]=d[c];i=i+1}}' session
echo ${GET[1]} ${GET[2]}
DESCRIPTION
The problem is the GET value printed outside is not the correct value ...
I understand your question as "how can I use the results of my awk script inside the shell where awk was called". The truth is that it isn't really trivial. You wouldn't expect to be able to use the output from a C program or python script easily inside your shell. Same with awk, which is a scripting language of its own.
There are some workarounds. For a robust solution, write your results from the awk script to a file in a suitably easy format and read them from the shell. As a hack, you could also try to ready the output from awk directly into the shell using $(). Combine that with the set command and you could do:
set -- $(awk <awk script here>)
and then use $1 $2 etc. but you have to be careful with spaces in the output from awk.
Related
Why AWK program's FS variable can be specified with -F flag of gawk (or other awk) interpreter/command?
Let me explain, AWK is a programming language and gawk is (one of many) an interpreter for AWK. gawk interpreter/execute/runs the AWK program that given to it. So why the FS (field separator) variable can be specified with gawk's -F flag? I find it kind of unnatural... and how does it technically do that?
My best guess as to "why" is as a convenience. FS is probably the most used/manipulated awk variable, so having a short option to set it is helpful
Consider
awk -F, '...' file.csv
# vs
awk 'BEGIN {FS=","} ...' file.csv
"How does it technically do that" -- see https://git.savannah.gnu.org/cgit/gawk.git/tree/main.c#n1586
Historically -F was implemented in gawk v1.01 so it would have existed in whatever legacy awk that gawk was based on.
Additionally, the POSIX specification mandates -F.
So why the FS (field separator) variable can be specified with gawk's
-F flag?
awk man page claims that
Command line variable assignment is most useful for dynamically
assigning values to the variables AWK uses to control how input is
broken into fields and records. It is also useful for controlling
state if multiple passes are needed over a single data file.
So -F comes handy when field separator is not etched in stone, but rather computed dynamically, as -F allows you tu use bash variable easily, imagine that you was tasked with developing part of bash script which should output last field of each line of file.txt when using character stored in variable sep as separator, then you could do that following way
awk -F ${sep} '{print $NF}' file.txt
find it kind of unnatural
This depend on what you have used before, cut user which want to get 3rd column from csv file might do that following way
cut -d , -f 3 file.csv
I am writing an awk script which needs to produce an output which needs to be sorted.
I am able to get the desired unsorted output in an awk array. I tried the following code to sort the array and it works and I don't know why and whether it is the expected behavior.
Sample Input to the question:
Ram,London,200
Alex,London,500
David,Birmingham,300
Axel,Mumbai,150
John,Seoul,450
Jen,Tokyo,600
Sarah,Tokyo,630
The expected output should be:
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230
The following script is required to show the city name along with the respective cumulative total of the integers present in the third field.
BEGIN{
FS = ","
OFS = ","
}
{
if($2 in arr){
arr[$2]+=$3;
}else{
arr[$2]=$3;
}
}
END{
for(i in arr){
print i,arr[i] | "sort"
}
}
The following code is in question:
for(i in arr){
print i,arr[i] | "sort"
}
The output of the print is piped to sort, which is a bash command.
So, how does this output travel from awk to bash?
Is this the expected behavior or a mere side effect?
Is there a better awk way to do it? Have tried asort and asorti already, but they exist with gawk and not awk.
PS: I am trying to specifically write a .awk file for the task, without using bash commands. Please suggest the same.
Addressing your specific questions in order:
So, how does this output travel from awk to bash?
A pipe to a spawned process.
Is this the expected behavior or a mere side effect?
Expected
Is there a better awk way to do it? Have tried asort and asorti already, but they exist with gawk and not awk.
Yes, pipe the output of the whole awk command to sort.
PS: I am trying to specifically write a .awk file for the task, without using bash commands. Please suggest the same.
See https://web.archive.org/web/20150928141114/http://awk.info/?Sorting for the implementation of a few common sorting algorithms in awk. See also https://rosettacode.org/wiki/Category:Sorting_Algorithms.
With respect to the question in your comments:
Since a process is spawned to sort from within the loop in the END rule, I was confused whether this will call the sort function on a single line and the spawned process will die there after, and a new process to sort will be spawned in the next iteration of the loop
The spawned process won't die until your awk script terminates or you call close("sort").
Could you please try changing you sort to sort -t',' -k1 in your code. Since your delimiter is comma so you need to inform sort that your delimiter is different than space. By default sort takes delimiter as comma.
Also you could remove if, else block ftom your main block and you could use only arr[$2]+=$3. Keep the rest code as it is apart from sort changes which I mentioned above
I am on mobile so couldn't paste all code but explanation should help you here.
What I would suggest is piping the output of awk to sort and not try and worry about piping the output within the END rule. While GNU awk provides asorti() to allow sorting the contents of an array, in this case since it is just the output you want sorted, a single pipe to sort after your awk script completes is all you need, e.g.
$ awk -F, -v OFS=, '{a[$2]+=$3}END{for(i in a)print i, a[i]}' file | sort
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230
And since it is a single pipe of the output, you incur no per-iteration overhead for the subshell required by the pipe.
If you want to avoid the pipe altogether, if you have bash, you can simply use process-substitution with redirection, e.g.
$ sort < <(awk -F, -v OFS=, '{a[$2]+=$3}END{for(i in a)print i, a[i]}' file)
(same result)
If you have GNU awk, then asorti() will sort a by index and you can place the sorted array in a new array b and then output the sorted results within the END rule, e.g.
$ awk -F, -v OFS=, '{a[$2]+=$3}END{asorti(a,b);for(i in b)print b[i], a[b[i]]}' file
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230
I have an awk command that returns the duplicates in an input stream with
awk '{a[$0]++}END{for (i in a)if (a[i]>1)print i;}'
However, I want to change the field separator characters and record separator characters before I do that. The command I use for that is
FS='\n' RS='\n\n'
Yet I'm having trouble making that happen. Is there a way to effectively combine these two commands into one? Piping one to the other doesn't seem to work either.
the action of BEGIN rule is executed before reading any input.
awk 'BEGIN{FS="\n";RS="\n\n"}{a[$0]++}END{for (i in a)if (a[i]>1)print i;}'
or you can specify them using command line options like:
awk -F '\n' -v RS='\n\n' '{a[$0]++}END{for (i in a)if (a[i]>1)print i;}'
I have the following code:
#!/bin/sh
while read line; do
printf "%s\n" $line
done < input.txt
Input.txt has the following lines:
one\two
eight\nine
The output is as follows
onetwo
eightnine
The "standard" solutions to retain the slashes would be to use read -r.
However, I have the following limitations:
must run under #!/bin/shfor reasons of portability/posix compliance.
not all systems
will support the -r switch to read under /sh
The input file format cannot be changed
Therefore, I am looking for another way to retain the backslash after reading in the line. I have come up with one working solution, which is to use sed to replace the \ with some other value (e.g.||) into a temporary file (thus bypassing my last requirement above) then, after reading them in use sed again to transform it back. Like so:
#!/bin/sh
sed -e 's/[\/&]/||/g' input.txt > tempfile.txt
while read line; do
printf "%s\n" $line | sed -e 's/||/\\/g'
done < tempfile.txt
I'm thinking there has to be a more "graceful" way of doing this.
Some ideas:
1) Use command substitution to store this into a variable instead of a file. Problem - I'm not sure command substitution will be portable here either and my attempts at using a variable instead of a file were unsuccessful. Regardless, file or variable the base solution is really the same (two substitutions).
2) Use IFS somehow? I've investigated a little, but not sure that can help in this issue.
3) ???
What are some better ways to handle this given my constraints?
Thanks
Your constraints seem a little strict. Here's a piece of code I jotted down(I'm not too sure of how valuable your while loop is for the other stuffs you would like to do, so I removed it off just for ease). I don't guarantee this code to be robustness. But anyway, the logic would give you hints in the direction you may wish to proceed. (temp.dat is the input file)
#!/bin/sh
var1="$(cut -d\\ -f1 temp.dat)"
var2="$(cut -d\\ -f2 temp.dat)"
iter=1
set -- $var2
for x in $var1;do
if [ "$iter" -eq 1 ];then
echo $x "\\" $1
else
echo $x "\\" $2
fi
iter=$((iter+1))
done
As Larry Wall once said, writing a portable shell is easier than writing a portable shell script.
perl -lne 'print $_' input.txt
The simplest possible Perl script is simpler still, but I imagine you'll want to do something with $_ before printing it.
first post here, but been a lurker for ages. i have googled for ages, but cant find what i want (many abigious topic subjects which dont request what the topic suggests it does ...). not new to awk or scripting, just a little rusty :)
i'm trying to write an awk script which will set shell env values as it runs - for another bash script to pick up and use later on. i cannot simply use stdout from awk to report this value i want setting (i.e. "export whatever=awk cmd here"), as thats already directed to a 'results file' which the awkscript is creating (plus i have more than one variable to export in the final code anyway).
As an example test script, to demo my issue:
echo $MYSCRIPT_RESULT # returns nothing, not currently set
echo | awk -f scriptfile.awk # do whatever, setting MYSCRIPT_RESULT as we go
echo $MYSCRIPT_RESULT # desired: returns the env value set in scriptfile.awk
within scriptfile.awk, i have tried (without sucess)
1/) building and executing an adhoc string directly:
{
cmdline="export MYSCRIPT_RESULT=1"
cmdline
}
2/) using the system function:
{
cmdline="export MYSCRIPT_RESULT=1"
system(cmdline)
}
... but these do not work. I suspect that these 2 commands are creating a subshell within the shell awk is executing from, and doing what i ask (proven by touching files as a test), but once the "cmd"/system calls have completed, the subshell dies, unfortunatley taking whatever i have set with it - so my env setting changes dont stick from "the caller of awk"'s perspective.
so my question is, how do you actually set env variables within awk directly, so that a calling process can access these env values after awk execution has completed? is it actually possible?
other than the adhoc/system ways above, which i have proven fail for me, i cannot see how this could be done (other than writing these values to a 'random' file somewhere to be picked up and read by the calling script, which imo is a little dirty anyway), hence, help!
all ideas/suggestions/comments welcomed!
You cannot change the environment of your parent process. If
MYSCRIPT_RESULT=$(awk stuff)
is unacceptable, what you are asking cannot be done.
You can also use something like is described at
Set variable in current shell from awk
unset var
var=99
declare $( echo "foobar" | awk '/foo/ {tmp="17"} END {print "var="tmp}' )
echo "var=$var"
var=
The awk END clause is essential otherwise if there are no matches to the pattern declare dumps the current environment to stdout and doesn't change the content of your variable.
Multiple values can be set by separating them with spaces.
declare a=1 b=2
echo -e "a=$a\nb=$b"
NOTE: declare is bash only, for other shells, use eval with the same syntax.
You can do this, but it's a bit of a kludge. Since awk does not allow redirection to a file descriptor, you can use a fifo or a regular file:
$ mkfifo fifo
$ echo MYSCRIPT_RESULT=1 | awk '{ print > "fifo" }' &
$ IFS== read var value < fifo
$ eval export $var=$value
It's not really necessary to split the var and value; you could just as easily have awk print the "export" and just eval the output directly.
I found a good answer. Encapsulate averything in a subshell!
The comand declare works as below:
#Creates 3 variables
declare var1=1 var2=2 var3=3
ex1:
#Exactly the same as above
$(awk 'BEGIN{var="declare "}{var=var"var1=1 var2=2 var3=3"}END{print var}')
I found some really interesting uses for this technique. In the next exemple I have several partitions with labels. I create variables using the labels as variable names and the device name as variable values.
ex2:
#Partition data
lsblk -o NAME,LABEL
NAME LABEL
sda
├─sda1
├─sda2
├─sda5 System
├─sda6 Data
└─sda7 Arch
#Creates a subshell to execute the text
$(\
#Pipe lsblk to awk
lsblk -o NAME,LABEL | awk \
#Initiate the variable with the text for the declare command
'BEGIN{txt="declare "}'\
#Filters devices with labels Arch or Data
'/Data|Arch/'\
#Concatenate txt with itself plus text for the variables(name and value)
#substr eliminates the special caracters before the device name
'{txt=txt$2"="substr($1,3)" "}'\
#AWK prints the text and the subshell execute as a command
'END{print txt}'\
)
The end result of this is 2 variables: Data with value sda6 and Arch with value sda7.
The same exemple in a single line.
$(lsblk -o NAME,LABEL | awk 'BEGIN{txt="declare "}/Data|Arch/{txt=txt$2"="substr($1,3)" "}END{print txt}')