Can I specify a default value to a variable in AWK like BASH in one statement using parameter substitution?
BASH example:
Code:
argument=${$1-"default if empty"} (BASH)
First, you have an extra dollar sign (shown in red above) that shouldn't be there.
Second: your default if empty string is misleading. With the form argument=${parm-word}, word is assigned only if parm is unset. If parm is set, but empty; argument will be set to the empty string.
To get what you probably intended (assign word if parm is set to an empty string or if parm is unset); you want:
Code:
argument=${1:-"default if unset or empty"}
Quote:
I know I can do:
Code:
argument=$1; sub ( "^$", "default if empty", argument) (AWK)
Mike
If I understand what you're trying to do (assign an awk variable the value of a shell variable if it is set and not empty, the easy way is to still use shell variable assignment:
Code:
awk -v argument=${1:-"default if unset or empty"} 'BEGIN{print argument}'
But, you can also do it entirely inside an awk script. Compare what happens with the following script:
Code:
#!/bin/ksh
date > now
awk -v v1="v1 -v" '
function setvars() {
v1 = v1 ? v1 : "v1 unset, empty string, or 0"
sub("^$", "v2 is unset or empty string", v2)
printf("fn=%d, FILENAME=\"%s\"\nv1=\"%s\"\nv2=\"%s\"\n\n",
fn, FILENAME, v1, v2)
}
BEGIN { setvars()
}
FNR == 1 {
fn++
setvars()
print fn, $0
print ""
}
END { print "in END clause"
setvars()
}' v2='v2 before 1st file operand' now v1= v2= now v1=0 v2=0 now v1=abc \
v2=def now v1='v1 after last file operand' v2=0
which, with any POSIX conforming shell such as bash or ksh (it has been tested with both) produces the output:
Code:
fn=0, FILENAME=""
v1="v1 -v"
v2="v2 is unset or empty string"
fn=1, FILENAME="now"
v1="v1 -v"
v2="v2 before 1st file operand"
1 Thu Apr 30 20:54:59 PDT 2015
fn=2, FILENAME="now"
v1="v1 unset, empty string, or 0"
v2="v2 is unset or empty string"
2 Thu Apr 30 20:54:59 PDT 2015
fn=3, FILENAME="now"
v1="v1 unset, empty string, or 0"
v2="0"
3 Thu Apr 30 20:54:59 PDT 2015
fn=4, FILENAME="now"
v1="abc"
v2="def"
4 Thu Apr 30 20:54:59 PDT 2015
in END clause
fn=4, FILENAME="now"
v1="v1 after last file operand"
v2="0"
If you want to try this on a Solaris/SunOS system, change awk to /usr/xpg4/bin/awk.
This User Gave Thanks to Don Cragun For This Post:
Thanks for pointing out the extra dollar sign. I made a typo while posting.
I am asking if there is an equivilent in awk to the BASH example (only awk variables involved--no shell variables involved).
Mike
I'm sorry my crystal ball didn't work.
Giving an awk expression with no context indicating whether the $1 you showed us in your awk expression is a shell command line variable or a field from an input line makes it hard to guess at what you're trying to do.
If you would show us an example of what you're really trying to do instead of giving us part of one line of an awk script and (making us guess at the context) is likely to get you suggestions that will come closer to doing what you want.
I thought the meaning of $1 was pretty unambiguous in AWK.
Here is a little more context:
Code:
while (getline < "'"$failListFile"'") { split( $0, a, ","); failMessage[a[1]a[2]a[3]a[4]a[5]]=a[8]
fs=a[6]; sub ( "^$", "0000 01 01 00 00 00", fs ); failStart[a[1]a[2]a[3]a[4]a[5]]=fs
fe=a[7]; sub ( "^$", "9999 12 31 23 59 59", fe ); failEnd[a[1]a[2]a[3]a[4]a[5]]=fe
Trying to do the assignment and default in a single command if possible (possibly analagous to parameter substitution in BASH, if such a thing exists in AWK).
Mike
Last edited by Michael Stora; 05-01-2015 at 02:32 AM..
I thought the meaning of $1 was pretty unambiguous in AWK.
Here is a little more context:
Code:
while (getline < "'"$failListFile"'") { split( $0, a, ","); failMessage[a[1]a[2]a[3]a[4]a[5]]=a[8]
fs=a[6]; sub ( "^$", "0000 01 01 00 00 00", fs ); failStart[a[1]a[2]a[3]a[4]a[5]]=fs
fe=a[7]; sub ( "^$", "9999 12 31 23 59 59", fe ); failEnd[a[1]a[2]a[3]a[4]a[5]]=fe
Trying to do the assignment and default in a single command if possible (possibly analagous to parameter substitution in BASH, if such a thing exists in AWK).
Mike
There is no invocation of awk in this script. There is a reference to a shell variable failListFile (or maybe it is a reference to the current line in awk since the undefined awk variable failListFile with a $ in front of it references the contents of the current input line). There are mismatched braces. There is no description of what you are trying to do with this awk and/or bash script. I have no idea what "assignment and default in a single command" you are trying to perform.
I have shown you (in a working shell script that invokes awk) how you can assign an awk variable in an awk script based on a variable left uninitialized by the shell, a variable initialized to an empty string by the shell, and a variable initialized to a non-empty string by the shell and use that inside an awk script to set an awk variable to a default value based on a couple of different conditions.
You haven't explained what you want to do that isn't being done by the sample script I showed you. Since I can't figure out what you're trying to do, I am afraid that I am unable to help you any further.
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05-01-2015
