I have defined a variable inside one of the shell script to create the file name with date value in it.
I used "date +%Y%m%d" command to insert the current date which was defined in date_val variable.
And I have defined the filename variable to have "${path}/sample_${date_val}.txt
For few days it was creating the file name properly as /programfiles/sample_20180308.txt
But today the filename was created without date as /programfiles/sample_.txt
When I try to execute the command "date +%Y%m%d" in linux, it is returning the correct value - 20180309.
Any idea why the filename was created without the date value ??? . I did not modify anything in my script too. So wondering what might have gone wrong.
Sample excerpt of my script is given below for easy understanding :
EDITED
path=/programfiles
date_val=$(date +%Y%m%d )
file_name=${path}/sample_${date_val}.txt
Although incredibly unlikely, it's certainly possible for date to fail, based on the source code. Under the covers, it calls either clock_gettime() or gettimeofday(), both of which can fail.
The date program will also refuse to output anything to standard output if the date from either of those two functions is out of range during the call to (which is possible if they fail).
It's also possible that the date program could "disappear" for various reasons, such as actually being hidden or permissions changed, or a shortage of resources like file handles when attempting to open the executable.
As mentioned, all these possibilities are a stretch, unlikely to happen in the real world.
If you want to handle the case where you get inadequate output from date, you can simply try until you get a valid one, something like (with the possibility of adding some limit to detect if it's never any good):
todaysDate="$(date +%Y%m%d)"
while [[ ! $x =~ ^[0-9]{8}$ ]] ; do
sleep 1
todaysDate="$(date +%Y%m%d)"
done
# todaysDate now guaranteed to be eight digits.
Related
I am currently working on a small command line interface tool that someone not very familiar with bash could run from their computer. I have changed content for confidentiality, however functionality has remained the same.
The user would be given a prompt
the user would then respond with their answer(s)
From this, I would be given two bits of information:
1.their responses now as individual variables
2.the number of variables that I have now been given: this value is now a variable as well
my current script is as follows
echo List your favorite car manufacturers
read $car1 $car2 $car3 #end user can list as many as they wish
for n in {1..$numberofmanufacturers} #finding the number of
variables/manufactures is my second question
do
echo car$n
done
I am wanting to allow for the user to enter as many car manufacturers as they please (1=<n), however I need each manufacturer to be a different variable. I also need to be able to automate the count of the number of manufacturers and have that value be its own new variable.
Would I be better suited for having the end user create a .txt file in which they list (vertically) their manufactures, thus forcing me to use wc -l to determine the number of manufacturers?
I appreciate any help in advance.
As I said in the comment, whenever you want to use multiple dynamically created variables, you should check if there isn't a better data structure for your use case; and in almost all cases there will be. Here is the implementation using bash arrays. It prints out the contents of the input array in three different ways.
echo List your favorite car manufacturers
# read in an array, split on spaces
read -a cars
echo Looping over array values
for car in "${cars[#]}"
do
echo $car
done
echo Looping over array indices
for i in ${!cars[#]}
do
echo ${cars[$i]}
done
echo Looping from 0 to length-1
let numcars=${#cars[#]}
for i in $(seq 0 $((numcars-1)))
do
echo ${cars[$i]}
done
I am basically trying to save to data/${EPOCH_TIME}:
begin_unix_time: "J"$first system "date +%s"
\t:1 save `data/"string"$"begin_unix_time"
I am expecting it to save to data/1578377178
You do not need to cast first system "date +%s" to a long in this case, since you want to attach one string to another. Instead you can use
begin_unix_time:first system "date +%s"
to store the string of numbers:
q)begin_unix_time
"1578377547"
q)`$"data/",begin_unix_time
`data/1578377547
Here you use the comma , to join one string to another, then using cast `$ to convert the string to a symbol.
The keyword save is saving global data to a file. Given your filepath, it looks like youre trying to save down a global variable named 1578377547, and kdb can not handle variable names being purely numbers.
You might want to try saving a variable named a1578377547 instead, for example. This would change the above line to
q)`$"data/a",begin_unix_time
`data/a1578377547
and your save would work correctly, given that the global variable a1578377547 exists. Because you are sourcing the date down to the second from linux directly in the line you are saving a variable down to, this will likely not work, due to time constantly changing!
Also note that the timer system command will repeat it the execution n times (as in \t:n), meaning that the same variable will save down mutliple times given the second does not change. The time will also likely change for large n and you wont have anything assigned to the global variable you are trying to save should the second change.
I'm new to bash and would like your help; couldn't find an answer for this case.
I'm trying to check if the files in one directory exist in another directory
Let's say I have the path /home/public/folder/ (here I have several files)
and I want to check if the files exist in /home/private/folder2
I tried that
for file in $firstPath/*
do
if [ -f $file ]; then
(ask if to over write etc.. rest of the code)
And also
for file in $firstPath/*
do
if [ -f $file/$secondPath ]; then
(ask if to over write etc.. rest of the code)
Both don't work; it seems that in the first case, it compares the files in the first path (so it always ask me if I want to overwrite although it doesn't exist in the second path)
And in the second case, it doesn't go inside the if statement.
How could I fix that?
When you have a construct like for file in $firstPath/*, the value of $file is going to include the value of $firstPath, which does not exist within $secondPath. You need to strip the path in order to get the bare filename.
In traditional POSIX shell, the canonical way to do this was with an external tool called basename. You can, however, achieve what is generally thought to be equivalent functionality using Parameter Expansion, thus:
for file in "$firstPath"/*; do
if [[ -f "$secondPath/${file##*/}" ]]; then
# file exists, do something
fi
done
The ${file##*/} bit is the important part here. Per the documentation linked above, this means "the $file variable, with everything up to the last / stripped out." The result should be the same as what basename produces.
As a general rule, you should quote your variables in bash. In addition, consider using [[ instead of [ unless you're actually writing POSIX shell scripts which need to be portable. You'll have a more extensive set of tests available to you, and more predictable handling of variables. There are other differences too.
I'm almost completely new to Linux programming, and Bash Scripts. I build an amateur radio AllStar node.
I'm trying to create a script that looks at a certain variable and based on that info decides if it should connect or not. I can use a command: asterisk -rx "rpt showvars 47168. This returns a list of variables and their current values. I can store the whole list into a variable that I define, in my test script I just called it MYVAR but I can't seem to only get the value of one of the variables that's listed.
I talked to someone who knows a lot about Linux programming, and she suggested that I try CONNECTED="${MYVAR[3]}" but when I do this, CONNECTED just seems to become a blank variable.
What really frustrates me is I have written programs in other programming languages, and I've been told Bash scripts are easy to learn, but yet I can't seem to get this.
So any help would be great.
how did you assigned your variable?
It seems to me that you want to work with an array, then:
#!/bin/bash
myvar=( $( asterisk -rx "rpt showvars 47168 ) )
echo ${mywar[3]} # this is your fourth element
echo ${#myvar[#]} # this is the total of element in your array
be careful that index in an array starts at 0
I have a cron task that runs periodically. This task depends on a condition to be valid in order to complete its processing. In case it matters this condition is just a SELECT for specific records in the database. If the condition is not satisfied (i.e the SELECT does not return the result set expected) then the script exits immediately.
This is bad as the condition would be valid soon enough (don't know how soon but it will be valid due to the run of another script).
So I would like somehow to make the script more robust. I thought of 2 solutions:
Put a while loop and sleep constantly until the condition is
valid. This should work but it has the downside that once the script
is in the loop, it is out of control. So I though to additionally
after waking up to check is a specific file exists. If it does it
"understands" that the user wants to "force" stop it.
Once the script figures out that the condition is not valid yet it
appends a script in crontab and stops. That seconds script
continually polls for the condition and if the condition is valid
then restart the first script to restart its processing. This solution to me it seems to work but I am not sure if it is a good solution. E.g. perhaps programatically modifying the crontab is a bad idea?
Anyway, I thought that perhaps this problem is common and could have a standard solution, much better than the 2 I came up with. Does anyone have a better proposal? Which from my ideas would be best? I am not very experienced with cron tasks so there could be things/problems I could be overseeing.
instead of programmatically appending the crontab, you might want to consider using at to schedule the job to run again at some time in the future. If the script determines that it cannot do its job now, it can simply schedule itself to run again a few minutes (or a few hours, as it may) later by way of an at command.
Following up from our conversation in comments, you can take advantage of conditional execution in a cron entry. Supposing you want to branch based on time of day, you might use the output from date.
For example: this would always invoke the first command, then invoke the second command only if the clock hour is currently 11:
echo 'ScriptA running' ; [ $(date +%H) == 11 ] && echo 'ScriptB running'
More examples!
To check the return value from the first command:
echo 'ScriptA' ; [ $? == 0 ] echo 'ScriptB'
To instead check the STDOUT, you can use as colon as a noop and branch by capturing output with the same $() construct we used with date:
: ; [ $(echo 'ScriptA') == 'ScriptA' ] && echo 'ScriptB'
One downside on the last example: STDOUT from the first command won't be printed to the console. You could capture it to a variable which you echo out, or write it to a file with tee, if that's important.