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).
Related
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 trying to replace the word in shell script with sed -e command but its not replacing , please help on that, i have tried the below
we have separate file in /data/docs/config.log, in that file there is a word ?account for example ,
username acc, passsword acc, ?account.name
this ?account word needs to be replaced with word 'GLOBAL' using sed -e command ,
reacc = GLOBAL
sed -e "s/?account/$reacc/g" /data/docs/config.log > /data/docs/newconfig.log
but here the file newconfig.log has created with 0 size , no output written to the file , its not replacing its an empty file,
the output should be username acc, passsword acc, GLOBAL.name in newconfig.log
Being the only person who can reproduce the problem, you are pretty much on your own. There are plenty of things you can do to analyze the problem, though.
Double-check the shell. Don't have blind faith in #!/bin/sh. In cygwin for example, /bin/sh is an alias for bash. Verify with: echo $SHELL
Check permissions and file system. Do you have rights to write to the output file? Is the disk full? Does cat /data/docs/config.log > /data/docs/newconfig.log work? Test again in a different folder.
Double-check the output file. Is it really empty, or is the file system just slow with updating the file size? Is sed really finished? Test without output redirection; see if the output is dumped to stdout.
Test with a small file; one or two lines is enough.
If even that does not work, then test sed itself. Who knows, maybe you have a weird alias that hides the real sed. The most trivial filter is sed -e '', which should simply echo every line you type (just like cat without parameters). Does that work? Then try some simple patterns.
Systematically iterate between test cases that succeed and test case that fail, until you have found the breaking point. Doing so, you should be able to find the cause. Sorry, that's all I can do for you right now.
Remove spaces around =. Try after making
reacc=GLOBAL
I'm trying to do a simple operation in ksh that I need to repeat in sh (Bourne shell)
All I want to do is append the contents of the first line of hte pay_period.txt file to the end of the new file name. This works great in ksh, but does not work in bourne. The program I'm using defaults to sh and I can't change that. Also I can't have actual shell scipts in the directories. So I have to issue commands.
How can I make the equivalent command below work in bourne
mv HEPAY.txt HE_PAY"$(/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).
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.
I need to create output files that include the input I'm providing. For example, a run of the program might look like:
Input command: do_things
Things have been done.
Input command: stop_doing_things
Things are no longer being done.
Where "do_things" and "stop_doing_things" are input from the user.
How can I output all of the above to a file using command prompt functions?
It's not clear what environment using "script " command linux will open a new shell and save everything done it to
This works for you, if you run it at last...
CMD > D:\mycmdout.txt
In that case, maybe you can capture your input as a variable. Echo the variable into the >> mycmdout.txt, then procede with the actual commands, again piped into >> mycmdout.txt as Sunny suggested.
SET /P variable=EnterInputHere
echo %variable% >> mycmdout.txt
EDIT: Be sure to use double >> as to append result to file.