This question already has answers here:
Brace expansion with variable? [duplicate]
(6 answers)
Closed 3 years ago.
I need to get user input for a number and then write a name row by row in linux terminal that much amount of times that user inputed. Example if I lets say chose a number 2 the program will write Name 2 times row by row. I wrote some code but I cant figure where is the mistake. I think its the loop where the mistake is.
echo "Please enter a number "
read $number
for value in {$number}
do
echo "Name"
done
To read input and save it into a variable named number, do:
read number
To get the value of number, do $number or ${number}. Remove the { } in the {$number} or shift $ with {.
Just do:
echo "Please enter a number "
read number
if ! test "$number" -gt 0 2> /dev/null; then
echo "You must enter an integer greater than 0" >&2
exit 1
fi
yes Name | sed ${number}q
But don't prompt for the number. Take it as a command line argument, and just do
yes Name | sed "${1}q"
Let sed generate the error message if the parameter is invalid.
The trouble with your loop is that for value in $number takes the string $number and breaks it on whitespace (depends on IFS, actually, but let's not get bogged down by details) and iterates over each value. That is, if $number is the string 1 3 dog 5, then the loop will iterate 4 times with $value taking the values 1, 3, dog, and 5. If $number is 7, then the loop iterates exactly once. You could do for((i=0; i < $number; i++)); do ..., but that does not generate any useful error message if $number is not an integer.
Related
This question already has answers here:
Why equal to operator does not work if it is not surrounded by space?
(4 answers)
How to compare strings in Bash
(12 answers)
Multiplication on command line terminal
(8 answers)
Closed 3 years ago.
I am in the very early stages of learning Unix scripting. I've written a Bash script which does not generate any errors, but clearly has a logic error, as the IF test always gives the same response.
I have tried various variations on the theme of my IF, but still end up with the same result.
#!/bin/bash
declare -i number1
declare -i number2
declare -i total
declare operation
echo "Enter a, s, m or d for add, subtract, multiply or divide"
read operation
echo "Enter number 1"
read number1
echo "Enter number 2"
read number2
echo "operation="$operation
if [ $operation=='m' ]
then
total=$number1*$number2
elif [ $operation=='a' ]
then
total=$number1+$number2
elif [ $operation=='d' ]
then
total=$number1/$number2
elif [ $operation=='s' ]
then
total=$number1-$number2
fi
echo $number1 " multiplied by " $number2 " equals " $total
exit 0
It doesn't matter whether I enter a, s or d (or indeed m) in response to the first prompt, my script always does a really nice multiplication... The line
echo "operation="$operation
correctly shows the operator I've requested.
Any ideas what I've done wrong?
Many thanks
You need to add spaces around all the ==. That's it. Instead of
if [ $operation=='m' ]
you should have:
if [ $operation == 'm' ]
Below is my requirement. I have a text file that has following content
File name - abc.txt
Content -
apple=0
mango=1
strawberry=10
I need to kick off the subsequent process only if any of the above stated variable has non zero values.
In this case, As two variables have values 1 and 10 respectively, I need to update an indicator - SKIP INDICATOR=N
If all variables have 0 as value, I need to update SKIP INDICATOR=Y
How to achieve this functionality in Linux. Kindly advise.
with very simple greps :
if [ $(grep '=' your_file | grep -v '=0') ]
then
echo "non zero values detected"
SKIP_INDICATOR=N
else
echo "all are zeroes"
SKIP_INDICATOR=Y
fi
Just note that this is a quick and dirty solution and it would NOT work properly if you have for example a=01 or a= 0 (eg with space)
Try:
grep -q '=0*[1-9]' textfile && skip_indicator=N || skip_indicator=Y
=0*[1-9] matches an '=' character followed by zero or more '0' characters followed by a digit in the range 1 to 9.
See Correct Bash and shell script variable capitalization for an explanation of why I changed SKIP_INDICATOR to skip_indicator.
#!/bin/bash
flag=`awk -F'=' '$NF!="0"{print;exit}' input`
if [ ! -z $flag ] ; then
SKIP_INDICATOR=N
echo "some variable value is different from 0. do something"
else
SKIP_INDICATOR=Y
echo "all variables have 0 as value. do another thing."
fi
exit 0
I'm trying to combine two lists containing names (if available) and emails with a standard email text in bash (shell)
(I had to delete the irrelevant code as it contains some private info, so some of the code might look unusal.)
The first half of the code checks if there is a name list along with the email list.
The second half combines only the email address and text if no name is available, if the name list is available it also 'tries' to combine the name, email and text.
f1 = email list and f2 = name list.
As you can see in the first half of the code below, $f2 should show the names if the list is available but it does not show anything in the log file.
I been trying to sort this problem out for two days but nothing has worked. When names are available it always outputs as "Hello ..." when it should be "Hello John D..."
#FIRST HALF
if [ "$names" = "no" ]
then
text="Hello..."
elif [ "$names" = "yes" ]
then
text="Hello $f2..."
fi
#SECOND HALF
if [ "$names" = "no" ]
then
for i in $(cat $emaillist); do
echo "$text" >> /root/log
echo "$i" >> /root/log
done
elif [ "$names" = "yes" ]
then
paste $emaillist $namelist | while IFS="$(printf '\t')" read -r f1 f2
do
echo "$text" >> /root/log
echo "$f1" >> /root/log
done
fi
When you run text="Hello $f2", $f2 is looked up at the time of the assignment; an exact string is assigned to text, and only that exact string is used later, on echo "$text".
This is very desirable behavior: If shell variables' values could run arbitrary code, it would be impossible to write shell scripts that handled untrusted data safely... but it does mean that implementing your program requires some changes.
If you want to defer evaluation (looking up the value of $f2 at expansion time rather than assignment), don't use a shell variable at all: Use a function instead.
case $names in
yes) write_greeting() { echo "Hello $name..."; };;
*) write_greeting() { echo "Hello..."; };;
esac
while read -r name <&3 && read -r email <&4; do
write_greeting
echo "$email"
done 3<"$namelist" 4<"$emaillist" >>/root/log
Some enhancements in the code above:
You don't need paste to read from two streams in lockstep; you can simply open them on different file descriptors (above, FDs 3 and 4 are chosen; only 0, 1 and 2 are reserved, so larger numbers could have been selected as well) with a separate read command for each.
Opening your output sink only once for the entire loop (by putting the redirection after the done) is far more efficient than re-opening it every time you want to write a single line.
Expansions, such as "$namelist" and "$emaillist", are always quoted; this makes code more reliable if dealing with filenames with unusual characters (including spaces and glob expressions), or if IFS is at a non-default value.
This is a shortened-version of a script for reading 8mm tapes from a EXB-8500 with an autoloader (only 10 tapes at a time maximum) attached. It dd's in tape data (straight binary) and saves it to files that are named after the tape's 4-digit number (exmaple D1002.dat) in both our main storage and our backup. During this time it's logging info and displaying its status in the terminal so we can see how far along it is.
#!/bin/bash
echo "Please enter number of tapes: [int]"
read i
j=1
until [ $i -lt $j ]
do
echo "What is the number of tape $j ?"
read Tape_$j
(( j += 1 ))
done
echo "Load tapes into the tower and press return when the drive is ready"
read a
j=1
until [ $i -lt $j ]
do
k="Tape_$j"
echo "tower1 $j D$(($k)) `date` Begin"
BEG=$j" "D$(($k))" "`date`" ""Begin"
echo "tower1 $j D$(($k)) `date` End"
END=$j" "D$(($k))" "`date`" ""End"
echo "$BEG $END"
echo "$BEG $END"
sleep 2
(( j += 1 ))
done
echo "tower1 done"
Everything was hunky-dory until we got under 1000 (startig at 0999). Error code was ./tower1: 0999: Value too great for base (error token is "0999"). Now I already realize that this is because the script is forcing octal values when I type in the leading 0, and I know I should insert a 10# somewhere in the script, but the question is: Where?
Also is there a way for me to just define Tape_$j as a string? I feel like that would clear up a lot of these problems
To get the error, run the script, define however many tapes you want (at least one, lol), and insert a leading 0 into the name of the tape
EXAMPLE:
./test
Please enter number of tapes: [int]
1
What is the number of tape 1?
0999
./test: 0999: Value too great for base (error token is "0999")
You don't want to use $k as a number, but as a string. You used the numeric expression to evaluate a variable value as a variable name. That's very bad practice.
Fortunately, you can use variable indirection in bash to achieve your goal. No numbers involved, no error thrown.
echo "tower1 $j ${!k} `date` Begin"
BEG=$j" "D${!k}" "`date`" ""Begin"
And similarly in other places.
This question already has answers here:
Variables in bash seq replacement ({1..10}) [duplicate]
(7 answers)
Brace expansion with a Bash variable - {0..$foo}
(5 answers)
Closed 8 years ago.
I'm making a program in bash that creates a histoplot, using numbers I have created. The numbers are stored as such (where the 1st number is how many words are on a line of a file, and the 2nd number is how many times this amount of words on a line comes up, in a given file.)
1 1
2 4
3 1
4 2
this should produce:
1 #
2 ####
3 #
4 ##
BUT the output I'm getting is:
1 #
2 #
3 #
4 #
however the for loop is not recognising that my variable "hashNo" is a number.
#!/bin/bash
if [ -e $f ] ; then
while read line
do
lineAmnt=${line% *}
hashNo=${line##* }
#VVVV Problem is this line here VVVV
for i in {1..$hashNo}
#This line ^^^^^^^ the {1..$hashNo}
do
hashes+="#"
done
printf "%4s" $lineAmnt
printf " $hashes\n"
hashes=""
done < $1
fi
the code works if I replace hashNo with a number (eg 4 makes 4 hashes in my output) but it needs to be able to change with each line (no all lines on a file will have the same amount of chars in them.
thanks for any help :D
A sequence expression in bash must be formed from either integers or characters, no parameter substitutions take place before hand. That's because, as per the bash doco:
The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion.
In other words, brace expansion (which includes the sequence expression form) happens first.
In any case, this cries out to be done as a function so that it can be done easily from anywhere, and also made more efficient:
#!/bin/bash
hashes() {
sz=$1
while [[ $sz -ge 10 ]]; do
printf "##########"
((sz -= 10))
done
while [[ $sz -gt 0 ]]; do
printf "#"
((sz--))
done
}
echo 1 "$(hashes 1)"
echo 2 "$(hashes 4)"
echo 3 "$(hashes 1)"
echo 4 "$(hashes 2)"
which outputs, as desired:
1 #
2 ####
3 #
4 ##
The use of the first loop (doing ten hashes at a time) will almost certainly be more efficient than adding one character at a time and you can, if you wish, do a size-50 loop before that for even more efficiencies if your values can be larger.
I tried this for (( i=1; i<=$hashNo; i++ )) for the for loop, it seems to be working
Your loop should be
for ((i=0; i<hashNo; i++))
do
hashes+="#"
done
Also you can stick with your loop by the use of eval and command substitution $()
for i in $(eval echo {1..$hashNo})
do
hashes+="#"
done