I'm trying to do a simple operation in ksh that I need to repeat in sh (Bourne shell)
All I want to do is append the contents of the first line of hte pay_period.txt file to the end of the new file name. This works great in ksh, but does not work in bourne. The program I'm using defaults to sh and I can't change that. Also I can't have actual shell scipts in the directories. So I have to issue commands.
How can I make the equivalent command below work in bourne
mv HEPAY.txt HE_PAY"$(/usr/bin/head -1 pay_period.txt)."txt
The results of $(/usr/bin/head -1 pay_period.txt) is 20140101.
If you are really talking about a real Bournce shell then you need to use backticks for command substitution ($() is POSIX and portable among "modern", POSIX-compliant shells but won't work in old, legacy shells), e.g.
mv HEPAY.txt HE_PAY`/usr/bin/head -1 pay_period.txt`.txt
Other than that I see no reason why this should not work.
PS: Note that head -1 isn't POSIX-compliant either (head -n 1 is).
Related
Here is temp/Makefile:
all:
echo $$PWD
echo $(CURDIR)
perl -e 'print $$ENV{"PWD"}'
and now
$make -C temp
make: Entering directory `/home/mgaleck/temp'
/home/mgaleck/temp
/home/mgaleck/temp
/home/mgaleck
make: Leaving directory `/home/mgaleck/temp'
Why is the third value without temp?
According to Make manual, -C option causes to "change the directory" (working directory?) first.
Same thing happens with Python.
Because the PWD environment variable doesn't hold the current working directory; it holds whatever the current working directory was the last time sh set it. Anything other than a shell starting up, or a shell executing the cd builtin (or a similar builtin like pushd, in shells that have it), has no effect on PWD, and relying on PWD anywhere except in the shell is probably a silly idea. Use getcwd (C), Cwd::getcwd (Perl), os.getcwd (Python), etc. instead.
I am basically looking for a way to do this
list=$(command)
while read -r arg
do
...
done <<< "$list"
Using sh intead of bash. The code as it is doesn't run because of the last line:
syntax error: unexpected redirection
Any fixes?
Edit: I need to edit variables and access them outside the loop, so using | is not acceptable (as it creates a sub-shell with independent scope)
Edit 2: This question is NOT similar to Why does my Bash counter reset after while loop as I am not using | (as I just noticed in the last edit). I am asking for another way of achiving it. (The answers to the linked question only explain why the problem happens but do not provide any solutions that work with sh (no bash).
There's no purely syntactic way to do this in POSIX sh. You'll need to use either a temporary file for the output of the command, or a named pipe.
mkfifo output
command > output &
while read -r arg; do
...
done < output
rm output
Any reason you can't do this? Should work .. unless you are assigning any variables inside the loop that you want visible when it's done.
command |
while read -r arg
do
...
done
I'm confronted with a rather strange problem an echo command causes in a script.
It's supposed to be really REALLY basic stuff, but still, there's something "off".
Suppose, I have this script:
#!/bin/bash
# SERVERPID='cat lite_server_pid.txt'
# kill -9 $SERVERPID
nohup java -Xmx3G -Xms2G -jar tekkit_lite_065.jar nogui > output.txt &
echo $! > lite_server_pid.txt
Yes, this starts my own little Minecraft/Tekkit-Server. ;-)
The Problem is, the file thats created is (for some reason) named
lite_server_pid.txt?
and YES, this includes the "?"! Doing the same command in shell, a file without ? is correctly created! Also, the content of the file is the desired processID.
Still, the ? following the filename is a major problem...
What am I doing wrong?
Check your file for DOS line endings. I suspect that ? is actually your terminal's attempt to display a carriage return (\r). Since bash expects UNIX-style newlines, the carriage return part of the DOS newline (\r\n) is treated as a legal character for the file name.
Run your script through dos2unix.
In bash shell scripting, I would typically run :> file to empty a file.
Now using fish, things are slightly different and the above command doesn't work.
What is fish equivalent?
Although it's not as short as :, true is a command that will work everywhere and produces no output:
true > file
Probably the easiest way that will be work in both Fish and Bash is to do echo "" > file
EDIT: Commenter was absolutely right echo "" > file produces a file with a newline, the correct command I was thinking of to create an empty file is cat /dev/null > file.
There is, and always was the magic method called touch which set change time to actual or create non-existent file. For compatiblity I suggest you to use this way in all scripts that you write (even if you write bash code).
I'm trying to do use the sed command in a shell script where I want to remove lines that read STARTremoveThisComment and lines that read removeThisCommentEND.
I'm able to do it when I copy it to a new file using
sed 's/STARTremoveThisComment//' > test
But how do I do this by using the same file as input and output?
sed -i (or the extended version, --in-place) will automate the process normally done with less advanced implementations, that of sending output to temporary file, then renaming that back to the original.
The -i is for in-place editing, and you can also provide a backup suffix for keeping a copy of the original:
sed -i.bak fileToChange
sed --in-place=.bak fileToChange
Both of those will keep the original file in fileToChange.bak.
Keep in mind that in-place editing may not be available in all sed implementations but it is in GNU sed which should be available on all variants of Linux, as per your tags.
If you're using a more primitive implementation, you can use something like:
cp oldfile oldfile.bak && sed 'whatever' oldfile >newfile && mv newfile oldfile
You can use the flag -i for in-place editing and the -e for specifying normal script expression:
sed -i -e 's/pattern_to_search/text_to_replace/' file.txt
To delete lines that match a certain pattern you can use the simpler syntax. Notice the d flag:
sed -i '/pattern_to_search/d' file.txt
You really should not use sed for that. This question seems to come up ridiculously often, and it seems very strange that it does since the general solution is so trivial. It seems bizarre that people want to know how to do it in sed, and in python, and in ruby, etc. If you want to have a filter operate on an input and overwrite it, use the following simple script:
#!/bin/sh -e
in=${1?No input file specified}
mv $in ${bak=.$in.bak}
shift
"$#" < $bak > $in
Put that in your path in an executable file name inline, and then the problem is solved in general. For example:
inline input-file sed -e s/foo/bar/g
Now, if you want to add logic to keep multiple backups, or if you have some options to change the backup naming scheme, or whatever, you fix it in one place. What's the command line option to get 1-up counters on the backup file when processing a file in-place with perl? What about with ruby? Is the option different for gnu-sed? How does awk handle it? The whole friggin' point of unix is that tools do one thing only. Handling logic for backup files is a second thing, and needs to be factored out. If you are implementing a tool, do not add logic to create backup files. Tell your users to use a 2nd tool for that. Integration is bad. Modularity is good. That is the unix way.
Notice that this script has several problems. The permissions/mode of the input file may be changed, for example. I'm sure there are innumerable other issues. However, by putting the backup logic in a wrapper script, you localize all of these issues and don't have to worry that sed overwrites the files and changes mode, while python keeps the file in place and does not change the inode (I made up those two cases, the point being that not all tools will use the same logic, while the wrapper script will.)
As far as I know it is not possible to use the same file for input and output. Though one solution is make a shell script which will save it to another file, delete the old input and rename the output to the input file name.
sed -e s/try/this/g input.file > output.file;mv output.file input.file
I suggest using sponge
sponge reads standard input and writes it out to the specified file.
Unlike a shell redirect, sponge soaks up all its input before writing
the output file. This allows constructing pipelines that read from and
write to the same file.
cat test | sed 's/STARTremoveThisComment//' | sponge test