如何在bash中将结果转换为整数

Question

当我这样做时

$ ls | wc -l
703

它给了我结果 703，我想打印 702 (703-1)

如何在 bash 中做到这一点？

Answer 1

（厚颜无耻的回答）在计数之前从输出中删除一行：D

ls | sed '1d' | wc -l

Answer 2

你可以使用算术扩展：

result=$(( $(ls | wc - l) - 1))

或者只是忽略其中一个文件

result=$(ls | tail -n+2 | wc -l)

请注意，如果文件名包含换行符，则它不起作用；在这种情况下，使用ls -q 每行获取一个文件名。如果您对文件的数量而不是文件名中的行数感兴趣，这也适用于第一个解决方案。

Answer 3

如何在bash中将结果转换为整数

@choroba 已经回答了这个问题，它应该已经解决了 OP 的问题。但是，我想在他的答案中添加更多内容。

OP 想要将结果转换为整数，但 Bash 没有像 Integer 这样的任何数据类型。

与许多其他编程语言不同，Bash 不按“类型”来隔离其变量。本质上，Bash 变量是字符串，但根据上下文，Bash 允许对变量进行算术运算和比较。决定因素是变量的值是否只包含数字。

请参阅 this 了解 Bash 中的算术运算。

请参阅this 以获得了解 Bash 无类型特性的最佳示例。我已经发布了下面的示例：

#!/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 $?