如何通過管道 wc -l 輸出到 echo 輸出

Question

我通過執行grep error logfile | wc -l計算日志文件中的grep error logfile | wc -l grep error logfile | wc -l

輸出 10

我想打印Error count found in logfile is 10

我認為需要通過 echo 將其通過管道傳輸，但是如何將 10 附加到 echo 輸出？

我試過

 var="$(grep -i error logfile | wc -l)" | echo "Error count found in logfile is $var"

Answer 1

您不應該將 var 輸入 echo，而是按順序運行它們：

var="$(grep -i error * | wc -l)"
echo "Error count found in logfile is $var"

或者您可以通過使用bash為 echo 命令定義變量：

 var="$(grep -i error * | wc -l)" ; echo "Error count found in logfile is $var"

---

正如下面的評論中所說，當然你可以在你的 echo 語句中嵌入你的命令調用：

echo "Error count found in logfile is $(grep -i error * | wc -l)"

Answer 2

簡單地嵌入（標准輸出）從一個字符串命令的輸出，而不需要還可以存儲在一個變量，它的輸出，只需使用一個命令替換（ $(...)在雙引號內的字符串（ "..." ） ：

echo "Error count found in logfile is $(grep error logfile | wc -l)"

正如Inian 的回答中所指出的， grep支持通過其-c選項直接計算匹配項，因此上述內容可以簡化為：

echo "Error count found in logfile is $(grep -c error logfile)"

僅當您稍后需要再次引用時才需要使用變量來存儲grep的輸出：

var=$(grep -c error logfile)
echo "Error count found in logfile is $var"
# ... use $var again as needed

---

至於你試過的： echo只接受命令行參數，不接受標准輸入，所以使用管道（ ... | echo ... ）是錯誤的方法。

Answer 3

使用帶有-c標志的printf和grep進行模式計數。

printf "Error count found in logfile is %s\n" "$(grep -chi error logfile)"

GNU grep使用的標志

-c, --count
       Suppress normal output; instead print a count of matching lines for each input file.  
       With the -v, --invert-match option  (see  below),  count  non-matching lines.

-h, --no-filename
       Suppress the prefixing of file names on output.  This is the default when there is 
       only one file (or only standard input) to search.

-i, --ignore-case
          Ignore case distinctions in both the PATTERN and the input files.

Answer 4

以下是處理此任務的不同方法的更多示例，只是為了幫助您了解 bash 的功能和選項：

(echo -en "Error count found in logfile is "; grep error logfile | wc -l)

{ printf "Error count found in logfile is " && wc -l < <(grep error logfile); }

printf 'Error count found in logfile is %d\\n' $(grep -c error logfile)

awk '/error/{++c} END{printf "Error count found in logfile is %d\\n", c}' logfile

var=$(grep -c error logfile); echo "Error count found in logfile is $var"

如果你想不遺余力地使用“here string”：

cat<<<"Error count found in logfile is $(grep -c error logfile)"

此外，這里有一個 bash 內置選項：

declare -i c=0
while read l; do
  [[ $l == *error* ]] && ((++c))
done < logfile
echo "Error count found in logfile is $c"`

Answer 5

使用撇號。

var=`cat x.dat | grep error | wc -l`
echo $var

Answer 6

echo "Error count found in logfile is "$(grep error logfile | wc -l)