I am writing a long bash script under CentOS 7 where perl is used for
manipulating some external files. So far I am using perl one-liners to do so but
ran into a problem when I need to append text to an external file.
Here is a simplified example in the bash script where txt is a bash variable
which I built containing a longish text with multiple newlines:
txt="a b$'\n'cd ef$'\n'g h$'\n'ij kl"
A simplified perl one-liner to append the text in the variable above to some
file in the bash script would be:
perl -pe 'eof && do{print $_'"${txt}"'; exit}'
someexternalfile.txt
This works when fine when $txt does /not/ contain any spaces but falls apart
when it does.
I would like to keep the above structure, ie using bash variables to build text
strings and one-liners to do the text manipulation. Hopefully there is a
"simple" solution to do this, I have tried many variations and failed
miserably... Note that I also want to use a similar pattern to do substitutions
in external files, I would thus like to use the same code pattern.
Thanks.
On 2022-01-30 20:12, H wrote:> I am writing a long bash script under CentOS 7 where perl is used for > manipulating some external files. So far I am using perl one-liners to > do so but ran into a problem when I need to append text to an external > file.Rewrite the whole thing in Perl. Over the years, I have rewritten scores of bash scripts in Perl, and they 1. execute much faster, 2. don't lose variables from while loops, 3. can use any of the thousands of CPAN modules, 4. can use libraries, and on and on. Todd Merriman Software Toolz
On 1/30/22 18:12, H wrote:> I am writing a long bash script under CentOS 7 where perl is used for manipulating some external files. So far I am using perl one-liners to do so but ran into a problem when I need to append text to an external file. > > Here is a simplified example in the bash script where txt is a bash variable which I built containing a longish text with multiple newlines: > > txt="a b$'\n'cd ef$'\n'g h$'\n'ij kl" > > A simplified perl one-liner to append the text in the variable above to some file in the bash script would be: > > perl -pe 'eof && do{print $_'"${txt}"'; exit}' someexternalfile.txt > > This works when fine when $txt does /not/ contain any spaces but falls apart when it does. > > I would like to keep the above structure, ie using bash variables to build text strings and one-liners to do the text manipulation. Hopefully there is a "simple" solution to do this, I have tried many variations and failed miserably... Note that I also want to use a similar pattern to do substitutions in external files, I would thus like to use the same code pattern.I don't understand why: echo -e $txt >> someexternalfile.txt doesn't do what you want, or if perl is absolutely what you need: perl -e "print \"${txt}\";" >> someexternalfile.txt I have no idea if you are trying to output literal $'s or 's or not. -- Orion Poplawski he/him/his - surely the least important thing about me Manager of NWRA Technical Systems 720-772-5637 NWRA, Boulder/CoRA Office FAX: 303-415-9702 3380 Mitchell Lane orion at nwra.com Boulder, CO 80301 https://www.nwra.com/
On 01/30/2022 11:00 PM, Orion Poplawski wrote:> On 1/30/22 18:12, H wrote: >> I am writing a long bash script under CentOS 7 where perl is used for manipulating some external files. So far I am using perl one-liners to do so but ran into a problem when I need to append text to an external file. >> >> Here is a simplified example in the bash script where txt is a bash variable which I built containing a longish text with multiple newlines: >> >> txt="a b$'\n'cd ef$'\n'g h$'\n'ij kl" >> >> A simplified perl one-liner to append the text in the variable above to some file in the bash script would be: >> >> perl -pe 'eof && do{print $_'"${txt}"'; exit}' someexternalfile.txt >> >> This works when fine when $txt does /not/ contain any spaces but falls apart when it does. >> >> I would like to keep the above structure, ie using bash variables to build text strings and one-liners to do the text manipulation. Hopefully there is a "simple" solution to do this, I have tried many variations and failed miserably... Note that I also want to use a similar pattern to do substitutions in external files, I would thus like to use the same code pattern. > > I don't understand why: > > echo -e $txt >> someexternalfile.txt > > doesn't do what you want, or if perl is absolutely what you need: > > perl -e "print \"${txt}\";" >> someexternalfile.txt > > I have no idea if you are trying to output literal $'s or 's or not. >Thank you, it works! I had forgotten to escape the quotes around my bash variable...
On 1/30/22 17:12, H wrote:> I am writing a long bash script under CentOS 7 where perl is used for manipulating some external files. So far I am using perl one-liners to do so but ran into a problem when I need to append text to an external file. > > Here is a simplified example in the bash script where txt is a bash variable which I built containing a longish text with multiple newlines: > > txt="a b$'\n'cd ef$'\n'g h$'\n'ij kl" > > A simplified perl one-liner to append the text in the variable above to some file in the bash script would be: > > perl -pe 'eof && do{print $_'"${txt}"'; exit}' someexternalfile.txt > > This works when fine when $txt does /not/ contain any spaces but falls apart when it does. > > I would like to keep the above structure, ie using bash variables to build text strings and one-liners to do the text manipulation. Hopefully there is a "simple" solution to do this, I have tried many variations and failed miserably... Note that I also want to use a similar pattern to do substitutions in external files, I would thus like to use the same code pattern. > > Thanks.On 2/2/22 17:54, H wrote: > I am still having a problem. The following (where $txt is an arbitrary string) works: > > perl -e 'print '"\"${txt}\""';' > > The following does not work (I want to append the content of the $txt to the end of an existing file in-place): > > perl -i -pe 'eof && do{print $_''\"aaa\"''; exit}' somefile.txt > > but this does: > > perl -i -pe "eof && do{print $_""\"${txt}\""'; exit}' somefile.txt > > as does: > > perl -i -pe "eof && do{print $_""\"${txt}\"""; exit}" somefile.txt > > The difference is that the last two perl command strings use " rather than '. > > My questions are: > > - Why would not using single-quotes for parts of the perl command string work? > > - Is there any reason I should fight this or should I just go with double-quotes for all parts of the perl command string? Any downside? Remember, these are all in bash scripts and I am looking for a "pattern" to use for other, more complicated text substitutions, hence the use of perl. On 2/2/22 18:55, H wrote: > I see I made a mistake, the line: > > perl -i -pe 'eof && do{print $_''\"aaa\"''; exit}' somefile.txt > > should be: > > perl -i -pe 'eof && do{print $_''\"${txt}\"''; exit}' somefile.txt > > Related question, if the $txt string contains eg $ or another special character, what would be the best way of escaping it so it is not substituted by perl? AIUI you are looking for a Bash shell scripting (programming) technique that allows you to append content to a file using a Perl one-liner with data that is dynamically generated from Bash variable values, all inside a Bash script (?). Perhaps it would be simpler if you put the data into a file and then invoked the Perl one-liner with the data file filename as an argument: 2022-02-02 22:08:34 dpchrist at tinkywinky ~ $ cat somefile.txt this is the contents of somefile. some more contents. 2022-02-02 22:08:37 dpchrist at tinkywinky ~ $ cat centos-h.sh #!/bin/bash txt="... foo ..." echo "$txt" > tmp.txt perl -pe 's/foo/bar/g' tmp.txt >> somefile.txt 2022-02-02 22:08:46 dpchrist at tinkywinky ~ $ bash centos-h.sh 2022-02-02 22:08:53 dpchrist at tinkywinky ~ $ cat somefile.txt this is the contents of somefile. some more contents. ... bar ... David