linux下常用的计算命令：
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[root@LAMP ~]# ((a=1+2**3-4%3)) [root@LAMP ~]# echo $a 8 [root@LAMP ~]# b=$((1+2**3-4%3)) [root@LAMP ~]# echo $b 8 [root@LAMP ~]# echo $((a+=1)) 9 [root@LAMP ~]# echo $((a*=2)) 18 [root@LAMP ~]# echo $a 18 [root@LAMP ~]# echo $((a%=2)) 0 [root@LAMP ~]# echo $((a+=8)) 8 [root@LAMP ~]# echo $((a/=2)) 4 [root@LAMP ~]# echo $((a++)) 4 [root@LAMP ~]# echo $a 5 [root@LAMP ~]# echo $((a++)) 5 [root@LAMP ~]# echo $a 6 [root@LAMP ~]# echo $((a--)) 6 [root@LAMP ~]# echo $a 5 [root@LAMP ~]# echo $((++a)) 6 [root@LAMP ~]# echo $a 6 [root@LAMP ~]# echo $((--a)) 5 [root@LAMP ~]# echo $a 5 [root@LAMP ~]# echo $((3>1)) 1 [root@LAMP ~]# echo $((3<1)) 0 [root@LAMP script]# i=2 [root@LAMP script]# let i=i*3 [root@LAMP script]# echo $i 6 [root@LAMP script]# expr length "byrd" 4 [root@LAMP script]# expr substr "byrd" 2 2 yr [root@LAMP test]# seq -s " " 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 [root@LAMP test]# echo ${#chars} 291 [root@LAMP test]# echo $(expr length "$chars") 291 [root@LAMP test]# expr length "$chars" 291 [root@LAMP test]# echo {chars}|wc -L 291 [root@LAMP test]# time for i in $(seq 50000);do count=`echo ${#chars}`;done; real 0m22.605s user 0m1.416s sys 0m5.814s [root@LAMP test]# time for i in $(seq 50000);do count=`echo {chars}|wc -m`;done; real 1m25.007s user 0m2.362s sys 0m8.060s [root@LAMP test]# time for i in $(seq 50000);do count=`expr length "{chars}"`;done; real 0m46.205s user 0m2.646s sys 0m10.198s [root@LAMP test]# time for i in $(seq 50000);do count=`echo expr length "{chars}"`;done; real 0m25.122s user 0m1.794s sys 0m6.744s [root@LAMP test]# time for i in $(seq 50000);do count=`expr length "{chars}"`;done; real 0m46.836s user 0m3.100s sys 0m10.740s [root@LAMP test]# time for i in $(seq 50000);do count=`echo {chars}|wc -L`;done; real 1m31.203s user 0m3.148s sys 0m12.504s [root@LAMP test]# echo "obase=2;205"|bc 11001101 [root@LAMP test]# echo "obase=8;205"|bc 315 [root@LAMP test]# echo "obase=10;205"|bc 205 [root@LAMP test]# echo "obase=16;205"|bc CD [root@LAMP test]# seq -s "+" 100 1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+55+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70+71+72+73+74+75+76+77+78+79+80+81+82+83+84+85+86+87+88+89+90+91+92+93+94+95+96+97+98+99+100 [root@LAMP test]# seq -s "+" 100|bc 5050 [root@LAMP test]# echo {1..100} 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 [root@LAMP test]# echo {1..100}|tr " " "+" 1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+55+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70+71+72+73+74+75+76+77+78+79+80+81+82+83+84+85+86+87+88+89+90+91+92+93+94+95+96+97+98+99+100 [root@LAMP test]# echo {1..100}|tr " " "+"|bc 5050 [root@LAMP test]# typeset -i A=1 B=3 [root@LAMP test]# A=A+B [root@LAMP test]# echo $A 4 [root@LAMP test]# echo $[2+3] 5 [root@LAMP test]# echo $[ 2 + 3 ] |
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