Here's my problem, from console if I type the below,
var=`history 1`
echo $var
I get the desired output. But when I do the same inside a shell script, it is not showing any output. Also, for other commands like pwd, ls etc, the script shows the desired output without any issue.
As value of variable contains space, add quotes around it.
E.g.:
var='history 1'
echo $var
I believe all you need is this as follows:
1- Ask user for the number till which user need to print the history in script.
2- Run the script and take Input from user and get the output as follows:
cat get_history.ksh
echo "Enter the line number of history which you want to get.."
read number
if [[ $# -eq 0 ]]
then
echo "Usage of script: get_history.ksh number_of_lines"
exit
else
history "$number"
fi
Added logic where it will check arguments if number of arguments passed is 0 then it will exit from script then.
By default history is turned off in a script, therefore you need to turn it on:
set -o history
var=$(history 1)
echo "$var"
Note the preferred use of $( ) rather than the deprecated backticks.
However, this will only look at the history of the current process, that is this shell script, so it is fairly useless.
Related
I need to add new lines with specific information to one or multiple files at the same time.
I tried to automate this task using the following script:
for i in /apps/data/FILE*
do
echo "nice weather 20190830 friday" >> $i
done
It does the job yet I wish I can automate it more and let the script ask me for to provide the file name and the line I want to add.
I expect the output to be like
enter file name : file01
enter line to add : IWISHIKNOW HOWTODOTHAT
Thank you everyone.
In order to read user input you can use
read user_input_file
read user_input_text
read user_input_line
You can print before the question as you like with echo -n:
echo -n "enter file name : "
read user_input_file
echo -n "enter line to add : "
read user_input_text
echo -n "enter line position : "
read user_input_line
In order to add line at the desired position you can "play" with head and tail
head -n $[$user_input_line - 1] $user_input_file > $new_file
echo $user_input_text >> $new_file
tail -n +$user_input_line $user_input_file >> $new_file
Requiring interactive input is horrible for automation. Make a command which accepts a message and a list of files to append to as command-line arguments instead.
#!/bin/sh
msg="$1"
shift
echo "$msg" | tee -a "$#"
Usage:
scriptname "today is a nice day" file1 file2 file3
The benefits for interactive use are obvious -- you get to use your shell's history mechanism and filename completion (usually bound to tab) but also it's much easier to build more complicated scripts on top of this one further on.
The design to put the message in the first command-line argument is baffling to newcomers, but allows for a very simple overall design where "the other arguments" (zero or more) are the files you want to manipulate. See how grep has this design, and sed, and many many other standard Unix commands.
You can use read statement to prompt for input,
read does make your script generic, but if you wish to automate it then you have to have an accompanying expect script to provide inputs to the read statement.
Instead you can take in arguments to the script which helps you in automation.. No prompting...
#!/usr/bin/env bash
[[ $# -ne 2 ]] && echo "print usage here" && exit 1
file=$1 && shift
con=$1
for i in `ls $file`
do
echo $con >> $i
done
To use:
./script.sh "<filename>" "<content>"
The quotes are important for the content so that the spaces in the content are considered to be part of it. For filenames use quotes so that the shell does not expand them before calling the script.
Example: ./script.sh "file*" "samdhaskdnf asdfjhasdf"
I often perform configuration changes using single line commands on Mac OS, Linux or even Windows and I want to easily log them in a file, so I can replay if I have to reconfigure the machine again.
Please not that I want to do these only for some commands, so the shell history is of not use.
Ideally I would like to be able to use some kind of shell extension that logs some of the commands.
As you know if you start your bash command with a space, this command is not logged into the history.
What if I can have another prefix that would do the opposite? Is there something there that can be used for this? A solution for bash would be more than enough and if there is an already existing solution it would much better than me writing a new one.
You could do your logging in PROMPT_COMMAND, extracting the specific commands from shell history and writing them to a file.
Something like:
log () {
last_command="$(history -p \!\!)"
if [[ $last_command == " "* ]] # save commands starting with *two* spaces
then
printf "%s\n" "$last_command" >> ~/special.log
fi
}
PROMPT_COMMAND="log; $PROMPT_COMMAND"
This has problems:
PROMPT_COMMAND is run each time the prompt is printed. Just pressing Enter multiple times could cause a command to be logged multiple times.
Marking with two spaces would, of course, need you to remove ignorespace or ignoreboth from HISTCONTROL so that commands starting spaces are logged at all.
AFAICT, history is updated when the next command is read, so the command is logged after the next command returns to the prompt, since that's when the correct history is available in PROMPT_COMMAND.
All this would be easier in zsh, with a preexec hook:
preexec () {
if [[ $1 == " "* ]]
then
printf "%s\n" "$1" >> ~/special.log
fi
}
The preexec function automatically gets the command as the first argument if history is enabled, saving us a deal of trouble. It is run when the command has been read, but before it begins execution, so the timing is perfect. From the documentation:
preexec
Executed just after a command has been read and is about to be
executed. If the history mechanism is active (regardless of whether
the line was discarded from the history buffer), the string that the
user typed is passed as the first argument, otherwise it is an empty
string. The actual command that will be executed (including expanded
aliases) is passed in two different forms: the second argument is a
single-line, size-limited version of the command (with things like
function bodies elided); the third argument contains the full text
that is being executed.
$ ls
$ echo foo | echo bar
bar
$ cat ~/special.log
ls
echo foo | echo bar
A function in .bashrc can be used like a prefix:
log_this_command () {
echo "$#" >> ~/a_log_file # log the command to file
"$#" # and run the command itself
}
Caveat: this only logs expanded arguments, rather than the raw input.
Source function with the same name function screencapture {echo "used parms: $#"; command screencapture $#}
appending to log file function screencapture {echo "$(date) screencapture " $# >> ~/log.txt; command screencapture $#}
as one runs screencapture command, log entry is created and command executes as uninterfered
you could automate in creating these functions, if the list of them is like .... all of them
How to make all user input on command line as stdin for a program?
In my case, I want to replace certain words inputed by user. For example, every time user uses the word animal1, I want it received as goldfish. So it would look like this:
$ animal1
goldfish: command not found
I tried the following bash command
while read input
do
sed "s/animal2/zebra/g;s/animal1/goldfish/g" <<< "$input"
done
But it prompts for user input and does not return to bash. I want it to run while using bash command line.
Also, this allowed me to capture output only.
bash | sed 's/animal2/zebra/g;s/animal1/goldfish/g'
But not user input.
If I understand you correctly, sounds like you just need to set up some aliases:
$ alias animal1=goldfish
$ animal1
bash: goldfish: command not found
This allows the shell to be used interactively as usual but will make the substitutions you want.
You can add this alias definition to one of your startup files, commonly ~/.bashrc or ~/.profile, to have them take effect on any new shell that you open.
The solution provided by Tom Fenech is good, however, if you plan to add more features to the command you can use a function like the following:
animal1() {
echo "Welcome to the new user interface!"
goldfish
# other commands
}
and put it in the user ~/.bashrc or ~/.bash_profile
The output will be:
$>animal1
Welcome to the new user interface!
-bash: goldfish: command not found
By using this approach you can, for example, create a custom output message. In the following snippet I take the return vale from the command and process it word by word. Then I remove the -bash: part of the output and reconstruct the message and output it.
animal1() {
echo "Welcome to the new user interface!"
retval=$(goldfish 2>&1)
# Now retval stores the output of the command glodfish (both stdout and stderr)
# we can give it directly to the user
echo "Default return value"
echo "$retval"
echo
# or test the return value to do something
# here I build a custom message by removing the bash part
message=""
read -ra flds <<< "$retval"
for word in "${flds[#]}" #extract substring from the line
do
# remove bash
msg="$(echo "$word" | grep -v bash)"
# append each word to message
[[ msg ]] && message="$message $msg"
done
echo "Custom message"
echo "$message"
echo
}
Now the output would:
Welcome to the new user interface!
Default return value
-bash: goldfish: command not found
Custom message
goldfish: command not found
If you comment the lines that echoes the default return value then you get exactly the output you asked for.
I am trying to echo the last command run inside a bash script. I found a way to do it with some history,tail,head,sed which works fine when commands represent a specific line in my script from a parser standpoint. However under some circumstances I don't get the expected output, for instance when the command is inserted inside a case statement:
The script:
#!/bin/bash
set -o history
date
last=$(echo `history |tail -n2 |head -n1` | sed 's/[0-9]* //')
echo "last command is [$last]"
case "1" in
"1")
date
last=$(echo `history |tail -n2 |head -n1` | sed 's/[0-9]* //')
echo "last command is [$last]"
;;
esac
The output:
Tue May 24 12:36:04 CEST 2011
last command is [date]
Tue May 24 12:36:04 CEST 2011
last command is [echo "last command is [$last]"]
[Q] Can someone help me find a way to echo the last run command regardless of how/where this command is called within the bash script?
My answer
Despite the much appreciated contributions from my fellow SO'ers, I opted for writing a run function - which runs all its parameters as a single command and display the command and its error code when it fails - with the following benefits:
-I only need to prepend the commands I want to check with run which keeps them on one line and doesn't affect the conciseness of my script
-Whenever the script fails on one of these commands, the last output line of my script is a message that clearly displays which command fails along with its exit code, which makes debugging easier
Example script:
#!/bin/bash
die() { echo >&2 -e "\nERROR: $#\n"; exit 1; }
run() { "$#"; code=$?; [ $code -ne 0 ] && die "command [$*] failed with error code $code"; }
case "1" in
"1")
run ls /opt
run ls /wrong-dir
;;
esac
The output:
$ ./test.sh
apacheds google iptables
ls: cannot access /wrong-dir: No such file or directory
ERROR: command [ls /wrong-dir] failed with error code 2
I tested various commands with multiple arguments, bash variables as arguments, quoted arguments... and the run function didn't break them. The only issue I found so far is to run an echo which breaks but I do not plan to check my echos anyway.
Bash has built in features to access the last command executed. But that's the last whole command (e.g. the whole case command), not individual simple commands like you originally requested.
!:0 = the name of command executed.
!:1 = the first parameter of the previous command
!:4 = the fourth parameter of the previous command
!:* = all of the parameters of the previous command
!^ = the first parameter of the previous command (same as !:1)
!$ = the final parameter of the previous command
!:-3 = all parameters in range 0-3 (inclusive)
!:2-5 = all parameters in range 2-5 (inclusive)
!! = the previous command line
etc.
So, the simplest answer to the question is, in fact:
echo !!
...alternatively:
echo "Last command run was ["!:0"] with arguments ["!:*"]"
Try it yourself!
echo this is a test
echo !!
In a script, history expansion is turned off by default, you need to enable it with
set -o history -o histexpand
The command history is an interactive feature. Only complete commands are entered in the history. For example, the case construct is entered as a whole, when the shell has finished parsing it. Neither looking up the history with the history built-in (nor printing it through shell expansion (!:p)) does what you seem to want, which is to print invocations of simple commands.
The DEBUG trap lets you execute a command right before any simple command execution. A string version of the command to execute (with words separated by spaces) is available in the BASH_COMMAND variable.
trap 'previous_command=$this_command; this_command=$BASH_COMMAND' DEBUG
…
echo "last command is $previous_command"
Note that previous_command will change every time you run a command, so save it to a variable in order to use it. If you want to know the previous command's return status as well, save both in a single command.
cmd=$previous_command ret=$?
if [ $ret -ne 0 ]; then echo "$cmd failed with error code $ret"; fi
Furthermore, if you only want to abort on a failed commands, use set -e to make your script exit on the first failed command. You can display the last command from the EXIT trap.
set -e
trap 'echo "exit $? due to $previous_command"' EXIT
Note that if you're trying to trace your script to see what it's doing, forget all this and use set -x.
After reading the answer from Gilles, I decided to see if the $BASH_COMMAND var was also available (and the desired value) in an EXIT trap - and it is!
So, the following bash script works as expected:
#!/bin/bash
exit_trap () {
local lc="$BASH_COMMAND" rc=$?
echo "Command [$lc] exited with code [$rc]"
}
trap exit_trap EXIT
set -e
echo "foo"
false 12345
echo "bar"
The output is
foo
Command [false 12345] exited with code [1]
bar is never printed because set -e causes bash to exit the script when a command fails and the false command always fails (by definition). The 12345 passed to false is just there to show that the arguments to the failed command are captured as well (the false command ignores any arguments passed to it)
I was able to achieve this by using set -x in the main script (which makes the script print out every command that is executed) and writing a wrapper script which just shows the last line of output generated by set -x.
This is the main script:
#!/bin/bash
set -x
echo some command here
echo last command
And this is the wrapper script:
#!/bin/sh
./test.sh 2>&1 | grep '^\+' | tail -n 1 | sed -e 's/^\+ //'
Running the wrapper script produces this as output:
echo last command
history | tail -2 | head -1 | cut -c8-
tail -2 returns the last two command lines from history
head -1 returns just first line
cut -c8- returns just command line, removing PID and spaces.
There is a racecondition between the last command ($_) and last error ( $?) variables. If you try to store one of them in an own variable, both encountered new values already because of the set command. Actually, last command hasn't got any value at all in this case.
Here is what i did to store (nearly) both informations in own variables, so my bash script can determine if there was any error AND setting the title with the last run command:
# This construct is needed, because of a racecondition when trying to obtain
# both of last command and error. With this the information of last error is
# implied by the corresponding case while command is retrieved.
if [[ "${?}" == 0 && "${_}" != "" ]] ; then
# Last command MUST be retrieved first.
LASTCOMMAND="${_}" ;
RETURNSTATUS='✓' ;
elif [[ "${?}" == 0 && "${_}" == "" ]] ; then
LASTCOMMAND='unknown' ;
RETURNSTATUS='✓' ;
elif [[ "${?}" != 0 && "${_}" != "" ]] ; then
# Last command MUST be retrieved first.
LASTCOMMAND="${_}" ;
RETURNSTATUS='✗' ;
# Fixme: "$?" not changing state until command executed.
elif [[ "${?}" != 0 && "${_}" == "" ]] ; then
LASTCOMMAND='unknown' ;
RETURNSTATUS='✗' ;
# Fixme: "$?" not changing state until command executed.
fi
This script will retain the information, if an error occured and will obtain the last run command. Because of the racecondition i can not store the actual value. Besides, most commands actually don't even care for error noumbers, they just return something different from '0'. You'll notice that, if you use the errono extention of bash.
It should be possible with something like a "intern" script for bash, like in bash extention, but i'm not familiar with something like that and it wouldn't be compatible as well.
CORRECTION
I didn't think, that it was possible to retrieve both variables at the same time. Although i like the style of the code, i assumed it would be interpreted as two commands. This was wrong, so my answer devides down to:
# Because of a racecondition, both MUST be retrieved at the same time.
declare RETURNSTATUS="${?}" LASTCOMMAND="${_}" ;
if [[ "${RETURNSTATUS}" == 0 ]] ; then
declare RETURNSYMBOL='✓' ;
else
declare RETURNSYMBOL='✗' ;
fi
Although my post might not get any positive rating, i solved my problem myself, finally.
And this seems appropriate regarding the intial post. :)
I have a bash script that sources contents from another file. The contents of the other file are commands I would like to execute and compare the return value. Some of the commands are have multiple commands separated by either a semicolon (;) or by ampersands (&&) and I can't seem to make this work. To work on this, I created some test scripts as shown:
test.conf is the file being sourced by test
Example-1 (this works), My output is 2 seconds in difference
test.conf
CMD[1]="date"
test.sh
. test.conf
i=2
echo "$(${CMD[$i]})"
sleep 2
echo "$(${CMD[$i]})"
Example-2 (this does not work)
test.conf (same script as above)
CMD[1]="date;date"
Example-3 (tried this, it does not work either)
test.conf (same script as above)
CMD[1]="date && date"
I don't want my variable, CMD, to be inside tick marks because then, the commands would be executed at time of invocation of the source and I see no way of re-evaluating the variable.
This script essentially calls CMD on pass-1 to check something, if on pass-1 I get a false reading, I do some work in the script to correct the false reading and re-execute & re-evaluate the output of CMD; pass-2.
Here is an example. Here I'm checking to see if SSHD is running. If it's not running when I evaluate CMD[1] on pass-1, I will start it and re-evaluate CMD[1] again.
test.conf
CMD[1]=`pgrep -u root -d , sshd 1>/dev/null; echo $?`
So if I modify this for my test script, then test.conf becomes:
NOTE: Tick marks are not showing up but it's the key below the ~ mark on my keyboard.
CMD[1]=`date;date` or `date && date`
My script looks like this (to handle the tick marks)
. test.conf
i=2
echo "${CMD[$i]}"
sleep 2
echo "${CMD[$i]}"
I get the same date/time printed twice despite the 2 second delay. As such, CMD is not getting re-evaluate.
First of all, you should never use backticks unless you need to be compatible with an old shell that doesn't support $() - and only then.
Secondly, I don't understand why you're setting CMD[1] but then calling CMD[$i] with i set to 2.
Anyway, this is one way (and it's similar to part of Barry's answer):
CMD[1]='$(date;date)' # no backticks (remember - they carry Lime disease)
eval echo "${CMD[1]}" # or $i instead of 1
From the couple of lines of your question, I would have expected some approach like this:
#!/bin/bash
while read -r line; do
# munge $line
if eval "$line"; then
# success
else
# fail
fi
done
Where you have backticks in the source, you'll have to escape them to avoid evaluating them too early. Also, backticks aren't the only way to evaluate code - there is eval, as shown above. Maybe it's eval that you were looking for?
For example, this line:
CMD[1]=`pgrep -u root -d , sshd 1>/dev/null; echo $?`
Ought probably look more like this:
CMD[1]='`pgrep -u root -d , sshd 1>/dev/null; echo $?`'