when I do
$ ls | wc -l
703
It gave me the result 703, I want to print 702 (703-1)
How can I do it in bash?
You can use arithmetic expansion:
result=$(( $(ls | wc - l) - 1))
or just ignore one of the files
result=$(ls | tail -n+2 | wc -l)
Note that it doesn't work if filenames contain the newline character; use ls -q to get one filename per line in such a case. This applies to the first solution, too, if you're interested in the number of files and not the number of lines in their names.
(Cheeky answer) Remove one line from the output before counting :D
ls | sed '1d' | wc -l
How to convert result as Integer in bash
#choroba has already answered this question and it should have solved OP's problem. However, I want to add more to his answer.
The OP's wants to convert the result into Integer but Bash doesn't have any data type like Integer.
Unlike many other programming languages, Bash does not segregate its variables by "type." Essentially, Bash variables are character strings, but, depending on context, Bash permits arithmetic operations and comparisons on variables. The determining factor is whether the value of a variable contains only digits.
See this for arithmetic operation in Bash.
See this for a best example to learn the untyped nature of Bash. I have posted the example below:
#!/bin/bash
# int-or-string.sh
a=2334 # Integer.
let "a += 1"
echo "a = $a " # a = 2335
echo # Integer, still.
b=${a/23/BB} # Substitute "BB" for "23".
# This transforms $b into a string.
echo "b = $b" # b = BB35
declare -i b # Declaring it an integer doesn't help.
echo "b = $b" # b = BB35
let "b += 1" # BB35 + 1
echo "b = $b" # b = 1
echo # Bash sets the "integer value" of a string to 0.
c=BB34
echo "c = $c" # c = BB34
d=${c/BB/23} # Substitute "23" for "BB".
# This makes $d an integer.
echo "d = $d" # d = 2334
let "d += 1" # 2334 + 1
echo "d = $d" # d = 2335
echo
# What about null variables?
e='' # ... Or e="" ... Or e=
echo "e = $e" # e =
let "e += 1" # Arithmetic operations allowed on a null variable?
echo "e = $e" # e = 1
echo # Null variable transformed into an integer.
# What about undeclared variables?
echo "f = $f" # f =
let "f += 1" # Arithmetic operations allowed?
echo "f = $f" # f = 1
echo # Undeclared variable transformed into an integer.
#
# However ...
let "f /= $undecl_var" # Divide by zero?
# let: f /= : syntax error: operand expected (error token is " ")
# Syntax error! Variable $undecl_var is not set to zero here!
#
# But still ...
let "f /= 0"
# let: f /= 0: division by 0 (error token is "0")
# Expected behavior.
# Bash (usually) sets the "integer value" of null to zero
#+ when performing an arithmetic operation.
# But, don't try this at home, folks!
# It's undocumented and probably non-portable behavior.
# Conclusion: Variables in Bash are untyped,
#+ with all attendant consequences.
exit $?
Related
This is my very first shell script for a Unix class, this is one of the scripts I hope to submit for my final. However there are a few kinks I cannot seem to clear up, it seems to be arithmetic operation errors, and I can't seem to figure it out. Please be kind! thank you so much for your time.
lightgreen=`echo -en "\e[92m"
echo What are the values of a, b \& c?
LIGHTRED=`echo -en "\e[101m"
echo a value:
read a
echo b value:
read b
echo c value:
read c
discrim=$(($b**2 - 4*$a*$c))
sqrtd=$((sqrt($discrim) | bc ))
echo test $sqrtd
echo ${lightgreen}The discriminant is:${discrim}
#xone=$((( -$b + sqrt$discrim) / (2 * $a) | bc ))
#xtwo=$((( -$b - sqrt$discrim) / (2 * $a) | bc ))
xone=$((echo (-1*$b + sqrt($discrim)) / (2*$a) | bc ))
xtwo=$((echo (-1*$b - sqrt($discrim)) / (2*$a) | bc ))
echo ${lightgreen}The discriminant is:${discrim}
#if [$discrim -lt 0 ]
# echo $LIGHTRED There are no real solutions.
#
#
#
echo The two solutions are $xone $xtwo
I have tried to mess with the syntax a good amount, I'm not sure if it's the parentheses that mess me up or the sqrt function, I have tried to incorporate | bc but to no avail. Any help is greatly appreciated! :)
Don't hesitate to call man bash, man bc manual pages.
Use https://www.shellcheck.net/ to check your shell scripts.
Shellcheck also exists on command line and in Visual Studio Code with extension.
#! /usr/bin/env bash
# The first line is very important to now the name of the interpreter
# Always close " , ' , or ` sequences with same character
# Do not use old `...` syntax, replaced by $(...)
# Here, use $'...', to assign value with \... sequences
lightgreen=$'\e[92m'
lightred=$'\e[101m'
normal=$'\e[0m'
# It's better to put phrase between "..." or '...'
echo "What are the values of a, b & c?"
# Use read -p option to specify prompt
# Use read -r option to not act backslash as an escape character
read -p "a value: " -r a
read -p "b value: " -r b
read -p "c value: " -r c
# With bash only, it's only possible to use integer values
# discrim=$(($b**2 - 4*$a*$c))
# use bc instead
discrim=$(bc -l <<<"$b^2 - 4*$a*$c")
# The syntax:
# bc <<<"..."
# is equivalent to:
# echo "..." | bc
# but without pipe (|)
# Close the color change with normal return
echo "${lightgreen}The discriminant is: ${discrim}${normal}"
if [[ "${discrim:0:1}" == "-" ]]; then
echo "${lightred}There are no real solutions${normal}"
# ... complex ...
else
sqrtd=$(bc -l <<<"sqrt($discrim)")
echo "sqrt($discrim)=$sqrtd"
xone=$(bc -l <<<"(-1*$b + $sqrtd) / (2*$a)")
xtwo=$(bc -l <<<"(-1*$b - $sqrtd) / (2*$a)")
echo "The two solutions are: $xone and $xtwo"
fi
As we know, in bash programming the way to pass arguments is $1, ..., $N. However, I found it not easy to pass an array as an argument to a function which receives more than one argument. Here is one example:
f(){
x=($1)
y=$2
for i in "${x[#]}"
do
echo $i
done
....
}
a=("jfaldsj jflajds" "LAST")
b=NOEFLDJF
f "${a[#]}" $b
f "${a[*]}" $b
As described, function freceives two arguments: the first is assigned to x which is an array, the second to y.
f can be called in two ways. The first way use the "${a[#]}" as the first argument, and the result is:
jfaldsj
jflajds
The second way use the "${a[*]}" as the first argument, and the result is:
jfaldsj
jflajds
LAST
Neither result is as I wished. So, is there anyone having any idea about how to pass array between functions correctly?
You cannot pass an array, you can only pass its elements (i.e. the expanded array).
#!/bin/bash
function f() {
a=("$#")
((last_idx=${#a[#]} - 1))
b=${a[last_idx]}
unset a[last_idx]
for i in "${a[#]}" ; do
echo "$i"
done
echo "b: $b"
}
x=("one two" "LAST")
b='even more'
f "${x[#]}" "$b"
echo ===============
f "${x[*]}" "$b"
The other possibility would be to pass the array by name:
#!/bin/bash
function f() {
name=$1[#]
b=$2
a=("${!name}")
for i in "${a[#]}" ; do
echo "$i"
done
echo "b: $b"
}
x=("one two" "LAST")
b='even more'
f x "$b"
You can pass an array by name reference to a function in bash (since version 4.3+), by setting the -n attribute:
show_value () # array index
{
local -n myarray=$1
local idx=$2
echo "${myarray[$idx]}"
}
This works for indexed arrays:
$ shadock=(ga bu zo meu)
$ show_value shadock 2
zo
It also works for associative arrays:
$ declare -A days=([monday]=eggs [tuesday]=bread [sunday]=jam)
$ show_value days sunday
jam
See also nameref or declare -n in the man page.
You could pass the "scalar" value first. That would simplify things:
f(){
b=$1
shift
a=("$#")
for i in "${a[#]}"
do
echo $i
done
....
}
a=("jfaldsj jflajds" "LAST")
b=NOEFLDJF
f "$b" "${a[#]}"
At this point, you might as well use the array-ish positional params directly
f(){
b=$1
shift
for i in "$#" # or simply "for i; do"
do
echo $i
done
....
}
f "$b" "${a[#]}"
This will solve the issue of passing array to function:
#!/bin/bash
foo() {
string=$1
array=($#)
echo "array is ${array[#]}"
echo "array is ${array[1]}"
return
}
array=( one two three )
foo ${array[#]}
colors=( red green blue )
foo ${colors[#]}
Try like this
function parseArray {
array=("$#")
for data in "${array[#]}"
do
echo ${data}
done
}
array=("value" "value1")
parseArray "${array[#]}"
Pass the array as a function
array() {
echo "apple pear"
}
printArray() {
local argArray="${1}"
local array=($($argArray)) # where the magic happens. careful of the surrounding brackets.
for arrElement in "${array[#]}"; do
echo "${arrElement}"
done
}
printArray array
Here is an example where I receive 2 bash arrays into a function, as well as additional arguments after them. This pattern can be continued indefinitely for any number of bash arrays and any number of additional arguments, accommodating any input argument order, so long as the length of each bash array comes just before the elements of that array.
Function definition for print_two_arrays_plus_extra_args:
# Print all elements of a bash array.
# General form:
# print_one_array array1
# Example usage:
# print_one_array "${array1[#]}"
print_one_array() {
for element in "$#"; do
printf " %s\n" "$element"
done
}
# Print all elements of two bash arrays, plus two extra args at the end.
# General form (notice length MUST come before the array in order
# to be able to parse the args!):
# print_two_arrays_plus_extra_args array1_len array1 array2_len array2 \
# extra_arg1 extra_arg2
# Example usage:
# print_two_arrays_plus_extra_args "${#array1[#]}" "${array1[#]}" \
# "${#array2[#]}" "${array2[#]}" "hello" "world"
print_two_arrays_plus_extra_args() {
i=1
# Read array1_len into a variable
array1_len="${#:$i:1}"
((i++))
# Read array1 into a new array
array1=("${#:$i:$array1_len}")
((i += $array1_len))
# Read array2_len into a variable
array2_len="${#:$i:1}"
((i++))
# Read array2 into a new array
array2=("${#:$i:$array2_len}")
((i += $array2_len))
# You can now read the extra arguments all at once and gather them into a
# new array like this:
extra_args_array=("${#:$i}")
# OR you can read the extra arguments individually into their own variables
# one-by-one like this
extra_arg1="${#:$i:1}"
((i++))
extra_arg2="${#:$i:1}"
((i++))
# Print the output
echo "array1:"
print_one_array "${array1[#]}"
echo "array2:"
print_one_array "${array2[#]}"
echo "extra_arg1 = $extra_arg1"
echo "extra_arg2 = $extra_arg2"
echo "extra_args_array:"
print_one_array "${extra_args_array[#]}"
}
Example usage:
array1=()
array1+=("one")
array1+=("two")
array1+=("three")
array2=("four" "five" "six" "seven" "eight")
echo "Printing array1 and array2 plus some extra args"
# Note that `"${#array1[#]}"` is the array length (number of elements
# in the array), and `"${array1[#]}"` is the array (all of the elements
# in the array)
print_two_arrays_plus_extra_args "${#array1[#]}" "${array1[#]}" \
"${#array2[#]}" "${array2[#]}" "hello" "world"
Example Output:
Printing array1 and array2 plus some extra args
array1:
one
two
three
array2:
four
five
six
seven
eight
extra_arg1 = hello
extra_arg2 = world
extra_args_array:
hello
world
For further examples and detailed explanations of how this works, see my longer answer on this topic here: Passing arrays as parameters in bash
You can also create a json file with an array, and then parse that json file with jq
For example:
my-array.json:
{
"array": ["item1","item2"]
}
script.sh:
ARRAY=$(jq -r '."array"' $1 | tr -d '[],"')
And then call the script like:
script.sh ./path-to-json/my-array.json
Say I want to search for "ERROR" within a bunch of log files.
I want to print one line for every file that contains "ERROR".
In each line, I want to print the log file path on the left-most edge while the number of "ERROR" on the right-most edge.
I tried using:
printf "%-50s %d" $filePath $errorNumber
...but it's not perfect, since the black console can vary greatly, and the file path sometimes can be quite long.
Just for the pleasure of the eyes, but I am simply incapable of doing so.
Can anyone help me to solve this problem?
Using bash and printf:
printf "%-$(( COLUMNS - ${#errorNumber} ))s%s" \
"$filePath" "$errorNumber"
How it works:
$COLUMNS is the shell's terminal width.
printf does left alignment by putting a - after the %. So printf "%-25s%s\n" foo bar prints "foo", then 22 spaces, then "bar".
bash uses the # as a parameter length variable prefix, so if x=foo, then ${#x} is 3.
Fancy version, suppose the two variables are longer than will fit in one column; if so print them on as many lines as are needed:
printf "%-$(( COLUMNS * ( 1 + ( ${#filePath} + ${#errorNumber} ) / COLUMNS ) \
- ${#errorNumber} ))s%s" "$filePath" "$errorNumber"
Generalized to a function. Syntax is printfLR foo bar, or printfLR < file:
printfLR() { if [ "$1" ] ; then echo "$#" ; else cat ; fi |
while read l r ; do
printf "%-$(( ( 1 + ( ${#l} + ${#r} ) / COLUMNS ) \
* COLUMNS - ${#r} ))s%s" "$l" "$r"
done ; }
Test with:
# command line args
printfLR foo bar
# stdin
fortune | tr -s ' \t' '\n\n' | paste - - | printfLR
Script:
#!/bin/ksh
FILENAME=$1
while read RECORD VALUE
do
echo ${RECORD} ${VALUE} "X"
done <"$FILENAME"
input file:
A 1
B 2
The output of script:
X1
X2
If I remove from echo "x", e.g.
echo ${RECORD} ${VALUE}
I am getting
A 1
B 2
what is wrong?
Update:
If I do
echo "X" ${RECORD} ${VALUE}
it prints correctly:
X A 1
X B 2
and :
echo ${RECORD} "X"
also prints correctly, so i am guessing the issues is with VALUE that maybe contains return carriage symbol (as input file was created on windows)
adding this inside the loop:
VALUE=`echo $VALUE| tr -d '\r'`
solved the issue, if you have a better solution you are more than welcome.
There is a parameter expansion operator you can use to remove a character from the end of a value, if it is present.
VALUE=${VALUE%$'\r'}
This is handled in-shell, without needing to start a new process.
I have a bash program which extracts marks from a file that looks like this:
Jack ex1=5 ex2=3 quiz1=9 quiz2=10 exam=50
I want the code to execute such that when I input into terminal:
./program -ex1 -ex2 -ex3
Jack does not have an ex3 in his data, so an output of 0 will be returned:
Jack 5 3 0
how do I code my program to output 0 for each unrecognized argument?
If I understand what you are trying to do, it isn't that difficult. What you need to do is read each line into a name and the remainder into marks. (input is read from stdin)
Then for each argument given on the command line, check if the first part matches the beginning of any grade in marks (the left size of the = sign). If it does, then save the grade (right side of the = sign) and set the found flag to 1.
After checking all marks against the first argument, if the found flag is 1, output the grade, otherwise output 0. Repeat for all command line arguments. (and then for all students in file) Let me know if you have questions:
#!/bin/bash
declare -i found=0 # initialize variables
declare -i grade=0
while read -r name marks; do # read each line into name & marks
printf "%s" "$name" # print student name
for i in "$#"; do # for each command line argument
found=0 # reset found (flag) 0
for j in $marks; do # for each set of marks check for match
[ $i = -${j%=*} ] && { found=1; grade=${j#*=}; } # if match save grade
done
[ $found -eq 1 ] && printf " %d" $grade || printf " 0" # print grade or 0
done
printf "\n" # print newline
done
exit 0
Output
$ bash marks_check.sh -ex1 -ex2 -ex3 < dat/marks.txt
Jack 5 3 0